Factories can level up by producing items
Mods introducing new content into the game.
Furnaces, assembling machines, production chains.
When copying/pasting a leveled factory with modules it crashes. Might be only in editor mode.
It was in fact only in editor mode, specifically if instant blueprinting was turned on. I have submitted a Pull Request with the fix.
should be fixed in 0.6.7. Thank you for reporting and fixing the problem!