Mod and plugin list: https://gist.github.com/XakepSDK/ce738ae6fd4c51d38123168dd682e675
Forestry version: forestry_1.12.2-5.8.2.387

I'm pregenerating world with nucleus plugin, i'm getting error from forestry:

[Server thread/ERROR] [forestry]: tried to generate a hive in an unloaded area.

Is this ok?

You won't have any hives in those chunks. Potentially retrogen might solve that though.