Or at least its display is bugged, but buying the upgrade does not seem to do anything.
I'm on version "Currently: Synergism-v2.10.10: May 1, 2023: The Third-$TIME$.txt" (I think?)
I've exported my save here: https://pastebin.com/vYewzMKe
#Coin upgrade 4x4 multiplier display is empty
floral bay
potent harbor
the error is here (at least part of the error) https://github.com/Pseudo-Corp/SynergismOfficial/blob/3419e262859c34eca7244decb3bd0076b8793eb1/translations/en.json#L2085
the string doesn't contain a value reference
floral bay
So indeed just a display issue it seems. The code seems fine for the upgrade effect itself.
Thanks
Coin upgrade 4x4 English display is empty
potent harbor
i'm checking the other localizations, it doesn't appear to be limited to English
floral bay
Coin upgrade 4x4 multiplier display is empty
potent harbor
yeah, all of them are bugged, with the exception of Chinese