Version Information

Minecraft version: 1.12.2
Forge version: 1.12.2-forge-14.23.5.2854
Other mods (if applicable): vanilla dimention, and mod dimention

Steps to reproduce:

1. enter a portal in a normal world

Expected Behavior:
sending me to the other dimention

Actual Behavior:
crashing again and again

Link to crash log (if applicable - use a site such as hastebin:
crash-2021-01-16_03.54.27-server.txt

ps: wen a deactivate the mod it work, but it also generate a overworld that isn't on cubic chunck and go back to the overworld on cubic chunck, also i ddoesn't understant well thing so if in the end there was a button or something that fix everything i'm very sorry to have waiste your time ^^' anyway have a good day and thx

First the customspawner mod is incompatible with cubic chunks, but the actual crash issue can be fixed by disabling optimized compatibility generator option in cubic chunks config.