I get the following message on game start:

Nepodařilo se načíst mód "molten_plastic/prototypes/compat.lua:1635: attempt to index local 'purifier' (a nil value)
stack traceback:
molten_plastic/prototypes/compat.lua:1635: in main chunk
[C]: in function 'require'
molten_plastic/data.lua:5: in main chunk"

This started to happen after a recent update (did an update for all the mods)

Hey there,

your crash is very peculiar, your error report suggests you are playing with Krastorio 2: Spaced Out but don't have air purifiers.
I've added a sanity check to stop your error from occuring but I am rather curious if you have a mod that changes or removes air purifiers?

Thank you for the report!

I don't know really as I have a lot of other mods, mainly planetary ones. Is there an easy way to check it?

BTW the fix works, thx!

Don't bother, it might've just been something else screwing with load order. Glad it works for you now!