Valkyrien Skies and radium/canary are incompatible by default.
This can lead to a crash on game start or world load.
If your crash report mentions contains:
Mixin apply failed valkyrienskies-common.mixins.json:feature.poi.MixinPOIManager -> net.minecraft.world.entity.ai.village.poi.PoiManager
Then it’s because of this conflict.
Luckily, there’s a fix.
Simply add mixin.ai.poi=false to the file named lithium.properties. Yes, the file is called lithium even if you are using Radium.
However if you’re using Canary, then the file will be called canary.properties.
Make sure you don’t put a # at the start of the line you add to the properties file, that will disable the fix.