So I started a world with a bunch of different mods which are Twilight Forest, Biome's O Plenty, & Extra Biome's XL (not sure if orespawn or candyland could be causing it because there was already a conflict before I added them in but I'll include the configs anyway) are the only biome mods that I have. Unfortunately, I can't tell which mod is causing it. But in game (in chat), it would say
[TwilightForest] Biome ID Conflict Detected. Fix by editing the config file.
The configs of all the mods that could be causing it are:
Biome O Plenty (I changed these ID's before because there was a conflict which fixed it but the conflict came back)
I've somewhat looked at them but I'd probably mess the ID's up if I tried putting in new ID's since I'm not really sure how these things work. I appreciate it if anyone tries to help since it's an old version of Minecraft.