Hello! I'm not 100% sure where the origin of this bug is, as I've read through both mods mixins, and admiditly am a bit stumped as to where the issue could be stemming from, but when Continuty runs with either Better Nether or Better End (I've connfirmed that this issue doesn't happen with BClib), MinecraftClient.getInstance().world is null when the player doesn't have a screen open (inventory, furnace, pause menu, etc). I did the following tests to troubleshoot:

All results were on Fabric 0.16.10 on 1.20.1, and had Fabric API 0.92.3+1.20.1

• Contiuity 3.0.0+1.20.1

• BClib 3.0.14

• Better End 4.0.11
  result: null without open screen

• Contiuity 3.0.0+1.20.1

• BClib 3.0.14
  result: works as intended

• BClib 3.0.14

• Better End 4.0.11
  result: works as intended

• Contiuity 3.0.0+1.20.1

• BClib 3.0.14

• Better Nether 9.0.10
  result: null without open screen

I also tested this in a few modpacks as well, with the same results. It only had this issue when the 2 mods were together. I learned about this issue when a mod I released had an issue rendering a custom Item that relied on the world to render a special way when both mods were present. I tested it both with my mod, and a custom mod that only logged the value of the world to make sure it wasn't my mod's doing.