Thankfully it doesn't seem to have any impact on the actual game, but our Fabric server gives a NullPointerException when we fall out of the world in the End.

[12-Nov-2020 00:38:09] [INFO] nbanyan fell out of the world [12-Nov-2020 00:38:10] [FATAL] Error executing task on Server [12-Nov-2020 00:38:10] java.lang.NullPointerException: null [12-Nov-2020 00:38:10] at net.minecraft.class_3204.method_14051(class_3204.java:202) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.class_3898.method_18713(class_3898.java:2734) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.class_3215.method_14096(class_3215.java:467) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.class_3244.method_12063(class_3244.java:931) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.class_2828.method_12272(class_2828.java:122) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.class_2828$class_2829.method_11054(class_2828.java:56) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.class_2600.method_11072(class_2600.java:21) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.class_3738.run(class_3738.java:18) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.class_1255.method_18859(class_1255.java:144) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.class_4093.method_18859(class_4093.java:23) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.server.MinecraftServer.method_24306(MinecraftServer.java:761) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.server.MinecraftServer.method_18859(MinecraftServer.java:155) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.class_1255.method_16075(class_1255.java:118) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.server.MinecraftServer.method_20415(MinecraftServer.java:743) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.server.MinecraftServer.method_16075(MinecraftServer.java:737) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.class_1255.method_18857(class_1255.java:127) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.server.MinecraftServer.method_16208(MinecraftServer.java:722) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.server.MinecraftServer.method_29741(MinecraftServer.java:674) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at net.minecraft.server.MinecraftServer.method_29739(MinecraftServer.java:257) ~[intermediary-server.jar:?] [12-Nov-2020 00:38:10] at java.lang.Thread.run(Thread.java:748) [?:1.8.0_265] [12-Nov-2020 00:43:06] [Prisma] Saving server... [12-Nov-2020 00:43:06] [INFO] Saving the game (this may take a moment!) [12-Nov-2020 00:43:06] [INFO] Saved the game [12-Nov-2020 00:43:28] [INFO] someotherguy fell out of the world [12-Nov-2020 00:43:29] [FATAL] Error executing task on Server [12-Nov-2020 00:43:29] java.lang.NullPointerException: null [12-Nov-2020 00:43:29] at net.minecraft.class_3204.method_14051(class_3204.java:202) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.class_3898.method_18713(class_3898.java:2734) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.class_3215.method_14096(class_3215.java:467) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.class_3244.method_12063(class_3244.java:931) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.class_2828.method_12272(class_2828.java:122) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.class_2828$class_2829.method_11054(class_2828.java:56) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.class_2600.method_11072(class_2600.java:21) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.class_3738.run(class_3738.java:18) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.class_1255.method_18859(class_1255.java:144) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.class_4093.method_18859(class_4093.java:23) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.server.MinecraftServer.method_24306(MinecraftServer.java:761) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.server.MinecraftServer.method_18859(MinecraftServer.java:155) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.class_1255.method_16075(class_1255.java:118) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.server.MinecraftServer.method_20415(MinecraftServer.java:743) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.server.MinecraftServer.method_16075(MinecraftServer.java:737) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.class_1255.method_18857(class_1255.java:127) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.server.MinecraftServer.method_16208(MinecraftServer.java:722) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.server.MinecraftServer.method_29741(MinecraftServer.java:674) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at net.minecraft.server.MinecraftServer.method_29739(MinecraftServer.java:257) ~[intermediary-server.jar:?] [12-Nov-2020 00:43:29] at java.lang.Thread.run(Thread.java:748) [?:1.8.0_265] [12-Nov-2020 00:45:21] [INFO] someotherguy fell out of the world [12-Nov-2020 00:45:22] [FATAL] Error executing task on Server [12-Nov-2020 00:45:22] java.lang.NullPointerException: null [12-Nov-2020 00:45:22] at net.minecraft.class_3204.method_14051(class_3204.java:202) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_3898.method_18713(class_3898.java:2734) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_3215.method_14096(class_3215.java:467) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_3244.method_12063(class_3244.java:931) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_2828.method_12272(class_2828.java:122) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_2828$class_2829.method_11054(class_2828.java:56) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_2600.method_11072(class_2600.java:21) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_3738.run(class_3738.java:18) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_1255.method_18859(class_1255.java:144) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_4093.method_18859(class_4093.java:23) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_24306(MinecraftServer.java:761) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_18859(MinecraftServer.java:155) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_1255.method_16075(class_1255.java:118) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_20415(MinecraftServer.java:743) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_16075(MinecraftServer.java:737) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_1255.method_18857(class_1255.java:127) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_16208(MinecraftServer.java:722) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_29741(MinecraftServer.java:674) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_29739(MinecraftServer.java:257) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at java.lang.Thread.run(Thread.java:748) [?:1.8.0_265] [12-Nov-2020 00:45:22] [FATAL] Error executing task on Server [12-Nov-2020 00:45:22] java.lang.NullPointerException: null [12-Nov-2020 00:45:22] at net.minecraft.class_3204.method_14051(class_3204.java:202) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_3898.method_18713(class_3898.java:2734) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_3215.method_14096(class_3215.java:467) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_3244.method_12063(class_3244.java:931) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_2828.method_12272(class_2828.java:122) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_2828$class_2829.method_11054(class_2828.java:56) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_2600.method_11072(class_2600.java:21) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_3738.run(class_3738.java:18) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_1255.method_18859(class_1255.java:144) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_4093.method_18859(class_4093.java:23) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_24306(MinecraftServer.java:761) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_18859(MinecraftServer.java:155) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_1255.method_16075(class_1255.java:118) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_20415(MinecraftServer.java:743) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_16075(MinecraftServer.java:737) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.class_1255.method_18857(class_1255.java:127) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_16208(MinecraftServer.java:722) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_29741(MinecraftServer.java:674) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at net.minecraft.server.MinecraftServer.method_29739(MinecraftServer.java:257) ~[intermediary-server.jar:?] [12-Nov-2020 00:45:22] at java.lang.Thread.run(Thread.java:748) [?:1.8.0_265]

Hmm the only thing I could see causing that issue is lithium or inv view. I would try updating those mods.

If you do have further questions please ask on discord since this issue tracker is for fabric api and not issues with mods.

I don't see anything in the stacktrace leading me to believe anything was changed. Could you include a list of mods?

At the time we only had Fabric-API, invView, and Lithium installed.
Here's the server startup log from the same day.
[12:03:03] [main/INFO]: Loading for game Minecraft 1.16.4 [12:03:03] [main/INFO]: [FabricLoader] Loading 44 mods: [email protected]+872498413a, [email protected], [email protected]+a4467d2a3a, [email protected]+b50ffc7b3a, [email protected]+3fa9f7c53a, [email protected]+a4467d2a3a, [email protected]+build.214, [email protected]+c93221003a, [email protected]+a4467d2a3a, [email protected]+f8ac1db23a, [email protected]+, [email protected], [email protected]+045df74f3a, [email protected]+a89534ab3a, [email protected]+f8ac1db23a, [email protected]+b7f9825d3a, [email protected]+f8ac1db23a, [email protected]+a4467d2a3a, [email protected]+9f0fb4b83a, [email protected]+f8ac1db23a, [email protected]+f8ac1db23a, [email protected]+730711c63a, [email protected]+f8ac1db23a, [email protected]+facf3bbf3a, [email protected]+a4467d2a3a, [email protected]+059ea8663a, [email protected]+ac8e8c593a, [email protected]+f8ac1db23a, [email protected]+8367596d3a, [email protected]+a4467d2a3a, [email protected]+52d308363a, [email protected]+c6a8ea893a, [email protected]+74cc3b203a, [email protected]+b764ce993a, [email protected]+f8ac1db23a, [email protected]+432ea1883a, [email protected]+16acbe5b3a, [email protected]+1.16, [email protected]+f8ac1db23a, [email protected]+fb0d9b0e3a, [email protected]+a4467d2a3a, [email protected]+a4467d2a3a, [email protected]+e00ecb5f3a, [email protected] [12:03:04] [main/INFO]: SpongePowered MIXIN Subsystem Version=0.8.2 Source=file:/data/jar/custom.jar Service=Knot/Fabric Env=SERVER [12:03:06] [main/WARN]: @Mixin target net/minecraft/class_3898$class_3208 is public in fabric-networking-[12:03:15] [main/INFO]: Environment: authHost='https://authserver.mojang.com', accountsHost='https://api.mojang.com', sessionHost='https://sessionserver.mojang.com', servicesHost='https://api.minecraftservices.com', name='PROD' [12:03:16] [main/WARN]: Ambiguity between arguments [teleport, destination] and [teleport, targets] with inputs: [Player, 0123, @e, dd12be42-52a9-4a91-a8a1-11c01849e498] [12:03:16] [main/WARN]: Ambiguity between arguments [teleport, location] and [teleport, destination] with inputs: [0.1 -0.5 .9, 0 0 0] [12:03:16] [main/WARN]: Ambiguity between arguments [teleport, location] and [teleport, targets] with inputs: [0.1 -0.5 .9, 0 0 0] [12:03:16] [main/WARN]: Ambiguity between arguments [teleport, targets] and [teleport, destination] with inputs: [Player, 0123, dd12be42-52a9-4a91-a8a1-11c01849e498] [12:03:16] [main/WARN]: Ambiguity between arguments [teleport, targets, location] and [teleport, targets, destination] with inputs: [0.1 -0.5 .9, 0 0 0] [12:03:16] [main/INFO]: Reloading ResourceManager: Default, afk display v1.1.0.zip, anti enderman grief v1.1.0.zip, anti-creeper-grief-master.zip, coordinates hud v1.2.0.zip, durability ping v1.1.0.zip, multiplayer sleep v2.5.2.zip, unlock all recipes v2.0.0.zip, Fabric Tool Attribute API (v1) [12:03:18] [Worker-Main-12/INFO]: Loaded 7 recipes [12:03:19] [Worker-Main-12/INFO]: Loaded 1000 advancements [12:03:21] [main/INFO]: Applied 0 biome modifications to 0 of 79 new biomes in 1.562 ms [12:03:21] [Server thread/INFO]: Starting minecraft server version 1.16.4 [12:03:21] [Server thread/INFO]: Loading properties [12:03:21] [Server thread/INFO]: Default game type: SURVIVAL [12:03:21] [Server thread/INFO]: Generating keypair [12:03:22] [Server thread/INFO]: Starting Minecraft server on 139.99.139.72:25565 [12:03:22] [Server thread/INFO]: Using epoll channel type [12:03:22] [Server thread/INFO]: Preparing level "world" [12:03:23] [Server thread/INFO]: Preparing start region for dimension minecraft:overworld [12:03:26] [Server thread/INFO]: Preparing spawn area: 0% [12:03:26] [Server thread/INFO]: Preparing spawn area: 0% [12:03:26] [Server thread/INFO]: Preparing spawn area: 0% [12:03:26] [Server thread/INFO]: Preparing spawn area: 0% [12:03:26] [Server thread/INFO]: Preparing spawn area: 0% [12:03:26] [Server thread/INFO]: Preparing spawn area: 0% [12:03:26] [Server thread/INFO]: Preparing spawn area: 0% [12:03:26] [Server thread/INFO]: Preparing spawn area: 0% [12:03:27] [Server thread/INFO]: Preparing spawn area: 17% [12:03:28] [Server thread/INFO]: Time elapsed: 5709 ms [12:03:28] [Server thread/INFO]: Done (6.298s)! For help, type "help"