If I load the savegame I provided to you in a v5.7.11 game & go to my company's income statement, I get the exact screenshot I provided to you.
The current state of this savegame shows the problem, and seems reproducible every time I load it. Moreover, this game was started on v5.7.11, eliminating the possibility to invoke 'cross-version sheananigan'-alike long shots.
Some intel about the probable game state when the donation was made were already provided in a post before. If I were to be given leads to follow about what kind of information is required, I could try to remember it.
I don't understand what your developer wants me to provide. I cannot foresee a problem before it happens?
Maybe add checks for such imbalances and throw errors or log something somewhere (in game state + savegame or in log files) when such a generic situation happens?
I'd be happy to have access to the source code and dig for that myself, however all you sold was the game's compiled binaries & promises of support/evolution. I am thus completely dependent on your willingness...
If you can't/don't want to investigate this further in the current state, I'd be glad to trade the closure of this investigation for the ownership of the v5.7.11 source code.
