Is the financial trend indicator messed up for anyone?

I have a near 200k city which is essentially a set of neighbourhoods isolated from the highway separated by train and airplane lines for both passenger and cargo.

The money trend indicator goes up and down between +300 000/month (=24h) and -2 500 000/month... yet I'm consistently making money hand-over-fist jumping up about 20k every time it updates.

So IDK if it's a source of income like haulage fees for freight or ticket income from transit being more than reported, or if my municipal council is reporting low numbers to defraud the national government to give Rentlar City all the subsidy monies (which were around 2-4 million a month) and bankroll the transit system.

Any one have any ideas or thoughts?