when playing with both the hallow and TBO-classic world gen seems to turn striped between hallow biomes and vanilla biomes as pictured in

to reproduce have both The Hallow and tbo-classic, create a new world (as worlds created without tbo-classic are unaffected) and enter the hallow

fabric loader version: 0.6.4+build.169
fabric api version: fabric-api-0.4.1+build.245-1.14
The Hallow version: TheHallow-1.1.0-beta+1.14.4
Trinkets version: trinkets-2.1.1
Tbo-classic version: tbo-classic-1.0.0

I believe this would be on tbo-classic's side. It might not be properly checking which dimension it's injecting its biomes into.

all right posted an issue to TBO-Classic's issue tracker here valoeghese/TBOClassic#1 (comment)

Possibly a byte overflow 🤔

Yeah almost definitely a byte overflow. (Thanks for nothing, mojang chunk nbt storage!)
If you get spam of unknown biome id in the log that’ll confirm it

Though the spam of unknown biome id that I mentioned doesn’t appear in the saved logs if I remember correctly