Forge: 1.15.2-forge-31.1.44
Quark: r2.1-231

Quickly spamming with item share causes minecraft to kick you for spamming.
"[playername] lost connection: Kicked for spamming", player disappears... but is still connected, can place blocks (but not destroy them), kill other players etc. while being invisible and not appearing in [tab] menu.

When just "normally" spamming with text server kicks you properly.
However if you hold [shift + t] and move mouse over items in inventory server "kicks" you while leaving you in-game. As a... "ghost", each time game has to do something to you (apply hunger when running, hurting players/mobs etc.) an exception occurs:

[Server thread/FATAL] [net.minecraft.util.concurrent.ThreadTaskExecutor/]: Error executing task on Server java.lang.NullPointerException: null at net.minecraft.world.server.TicketManager.func_219367_b(SourceFile:201) ~[?:?] at net.minecraft.world.server.ChunkManager.func_219183_a(ChunkManager.java:858) ~[?:?] at net.minecraft.world.server.ServerChunkProvider.func_217221_a(SourceFile:479) ~[?:?] at net.minecraft.network.play.ServerPlayNetHandler.func_147347_a(ServerPlayNetHandler.java:765) ~[?:?] at net.minecraft.network.play.client.CPlayerPacket.func_148833_a(SourceFile:122) ~[?:?] at net.minecraft.network.play.client.CPlayerPacket$PositionRotationPacket.func_148833_a(SourceFile:18) ~[?:?] at net.minecraft.network.PacketThreadUtil.func_225383_a(SourceFile:21) ~[?:?] at net.minecraft.util.concurrent.TickDelayedTask.run(SourceFile:18) ~[?:?] at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213166_h(SourceFile:144) [?:?] at net.minecraft.util.concurrent.RecursiveEventLoop.func_213166_h(SourceFile:23) [?:?] at net.minecraft.server.MinecraftServer.func_213166_h(MinecraftServer.java:731) [?:?] at net.minecraft.server.MinecraftServer.func_213166_h(MinecraftServer.java:141) [?:?] at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213168_p(SourceFile:118) [?:?] at net.minecraft.server.MinecraftServer.func_213205_aW(MinecraftServer.java:714) [?:?] at net.minecraft.server.MinecraftServer.func_213168_p(MinecraftServer.java:708) [?:?] at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213160_bf(SourceFile:103) [?:?] at net.minecraft.server.MinecraftServer.func_213202_o(MinecraftServer.java:693) [?:?] at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:641) [?:?] at java.lang.Thread.run(Thread.java:748) [?:1.8.0_201]

(Does not work with op'ped players as Forge needs to kick (or "kick") you)
I don't know whether it is caused by Quark or Forge itself.

Hello! Quark's moved to 1.18 now-- unfortunately, this means that (unless your bug is critical and/or game-breaking), we're closing support for issues filed for versions prior to it (e.g. Quark on 1.16).

If your issue still occurs on 1.18, or if your issue happens to be rather critical (e.g. consistently crashing the game with no other mods present), please leave another note or open a new issue. Thanks for your cooperation!