Just thought I’d mention that this is still happening. I gave up on my original save and started a new game in 0.21.12. My funds are now broken again after about 6 game years and a very active airport. What seems to be happening is that the tally for $$$ In/Out for the current hour got stuck on that hour at some point, so the budget page shows a running total of all airline income & building expenditure since it broke. Here’s a screenshot of the budget - all of those construction expenses happened last year and obviously >1M/hour would be pretty impressive for just airline income 
I have a copy of this save but am going to wait until the devs have a chance to take a look before I send them more bug reports since I think they are pretty swamped and won’t get around to looking at this for awhile. Would be happy to provide the save to anyone else who’s interested to poke around.