Yep... this happened to me yesterday and I thought it was just good timing by the attacker. BUT it happened again today the very second that I withdrew 100,000,000. There is definitely something wrong with the timing. This is not an insider card thing. Here's the timeline of events.
1) Travel to my city
2) Withdraw 100,000,000
3) Try to purchase skyscraper immediately
4) Instead was told I have 100,000,000 but can't purchase because I need 100,000,000
5) Dismissed the alert and noticed my cash had already dropped to 44,000,000
So I quickly redeposited what was remaining but something was strange. I still had 100% health. I immediately looked at the activity logged and saw that "3 minutes ago" i was attacked multiple times by two cartels and lost 56,000,000 total. The thing is... I had JUST withdrawn the money. There was no dirty cash 3 minutes ago.
About a minute and a half into my fit of cursing the game THEN my health rapidly depleted from 100% down to 20%.
I won't be wasting another dime or minute on this piece of shit game.