The server seems to be crashing during Feature Placement (presumably during chunk generation?), and reading the crash-report https://mclo.gs/BLv5yAL the source appears to be this mod.

Is this a bug with this mod or could it be a compatibility issue with another?

I seen this before where people have reported that deleting the config files for repurposed structures fixed it. Like the configs went borked and caused the list of mobs for spawners to be null. Though it should crash but warn. I'll check that part out but you should try deleting the configs. let me know if that works or not!

actually wait a second. The code throwing the error is this one:
Objects.requireNonNull(world.getRegistryManager().get(Registry.BIOME_KEY).getKey(biome))

The fact this is throwing null means the biome in the actual world is not in the registry wtf. This is actually massively concerning as this means another mod is injecting the wrong biomes into the world instead of the copied version minecraft make specifically for worldgen.

Well, I do know biomes o plenty has this issue where they just need to update their biome provider to provide the correct versions of their biomes. This might be related to that. I'll test this theory when I get time. I'll also rework my code a bit to prevent the crash as best I can
Glitchfiend/BiomesOPlenty#1691

can you try v2.2.6 just released now and let me know if the crash is now gone? Also, thank you for reporting the crash too!

https://www.curseforge.com/minecraft/mc-mods/repurposed-structures/files/3075029

I suspect you're using an outdated version of Blame which is generating incorrect reports until I fixed it in 1.4.2.
https://www.curseforge.com/minecraft/mc-mods/blame/files/3074617

Try updating blame for that.

Now for the freezing, That's super odd. The game doesn't freeze when I try repurposed structures alone on a server so it shouldn't be for you. (Unless you're testing by removing BoP in a world already made with BoP. Removing Worldgen Mods like that tends to cause issues in already made worlds) After you update Blame, can you run 2.2.6 repurposed structures and then get the server to freeze. Then upload the latest.log file from the server?

I know it's a bit to do but the latest.log should help clear up what could be going on.

Using the new version only works if you have BoP installed. If you don't it freezes the server on world generation.

Rolling back to 2.2.5 allows the server to load but trips all sorts of biome errors.

https://pastebin.com/UEsMnQ1k

It's been a few days now and I just thought I'll check in. Are any of you still having issues or nah? If you are having issues, could any of you give me the latest.log file after getting the issue to occur?

We are no longer using bop in our modpack, so I can't comment on it. Our server is running smoothly on 1.16.3. Using TNP Limitless 3 modpack.

Ah well thank you for getting back to me! Since no other new people have raised the issue of the crash and I haven't reproduce it myself, I'll close this issue now. If it ever happens again, don't hesitate to open a new issue here and I'll try and help. :)