This sounds like the same bug described here ((Total Funds Bar frozen and not updating - #14 by stash)) and I’ve heard a couple other people discuss it on Discord. I ran into this again in 0.21.12. If you check your budget screen I think you’ll see that the “Airline Income” and “Building Costs” are just piling up forever and never adding/subtracting from your hourly total $$.
I did submit this as a bug about a week ago but haven’t heard back on it.