The save for 300 hours broke.
I tried to change the versions of the mod, to older ones, it did not help.

Error while applying migration: Factorissimo 2 - notnotmelon fork: 1.1.16.lua

factorissimo-2-notnotmelon/migrations/1.1.16.lua:3: bad argument #2 of 3 to 'index' (string expected, got number)
stack traceback:
[C]: in function '__index'
__factorissimo-2-notnotmelon/migrations/1.1.16.lua:3: in main chunk

Very strange issue
After some investigation, it seems like this could only happen if the same migration file was ran twice.
No idea how your save got into this state

I've fixed the issue in 1.2.22, your save should be playable in that version

(at the time of writing, I have not released 1.2.22. Expect this update today or tomorrow)