I've been getting this bug for awhile now, but I've been avoiding it by no exploring or just reloading the auto-save and trying again. This is at least older than the last two updates you've done so it is not a bug recently introduced. Error message as follows:
Error while running event big-factories::on_chunk_generated (ID 12)
big-factories/scripts/spawn.lua:46: attempt to index local 'proto' (a nil value)
stack traceback:
big-factories/scripts/spawn.lua:46: in function <big-factories/scripts/spawn.lua:33>
I have a few more mods installed than the other save file I was using, so it could easily be one of those. If you need a save just let me know.