I am running a custom pack, when I try to load in a schematic, it crashes.
lunatriuscore 1.12.2-1.2.0.42
schematica 1.12.2-1.8.0.167

Crash Log:
https://pastebin.com/CUSSXAMi

I believe the issue is due to chisels and bits, as I have included chisels and bits in my build.

It crashed because something else was modifying the tile entity list when the renderer was trying to get the active tile entity.

Does this happen every time you try to load the schematic?

No, only on the build that I was working on, I'm unsure why, but when I removed the chisels and bits windows I made, it doesn't crash when I save the schematic and load it. There are still other chisels and bits in the build tho, so I'm unsure why the windows with the build caused an crash.