I started to get recently this crash https://pastebin.com/ffSLMYtY. I use Minecraft 1.12.1 and Forge 14.22.1.2480.

More information on this, it's caused by autoreglib.

I just added skillable and autoreglib to my pack and get this crash.

Botania r1.10-347
AutoRegLib-1.3-13
Skillable-beta-7
forge-1.12.1-14.22.1.2478

Yep you're correct, trying to find out which right now.

Wonderful it's a combination of mods...

Ok so the crash is caused by a combination of mods, in short

Botania + Better with Mods + Immersive Engineering = crash

Botania + Better with Mods = no crash
Botania + Immersive = no crash

Immersive Engineering DOES ship Botania API
Better with Mods as far as I can tell does not ship any API (besides it's own).

For this test only I opened Immersive Engineering's Jar file and deleted the botania API and the crash went away.

Will log with IE.

Sorry for blaming autoreglib I updated to latest IE at the same time as adding in Skillable + auto so it threw me a curveball.

The problem is still not solved, the crash still occurs with the new version. https://pastebin.com/D2hE3P64

this is a bug in IE, nothing botania can do.
follow the IE bug linked above for details