Essential mod is known to sometimes cause networking issues, and in this case it appears to be an issue with Chunk Blocking. But it only happens to a connecting player, not the hosting player.

Thread Dump is attached.
2024-04-09-1.log

Another* essential incompatibility report: https://discord.com/channels/1061675558347489343/1228862187775328369/1228862187775328369

Also, of note, the hang happens at the first point ImmersiveMC interacts with a Minecraft level (or world in non-Mojmap land).

*: Has just occurred to me this is actually the same person lol. That said, this appears to be on 1.20.1 Fabric

Adding to the above, part of the stack trace is also in c2me so perhaps something is happening there. The part of c2me that gets caught here is https://github.com/RelativityMC/C2ME-fabric/blob/ver/1.20.1/c2me-base/src/main/java/com/ishland/c2me/base/mixin/priority/MixinServerChunkManager.java#L50