1. You sell a call credit spread. This is where you sell a call at say $100 and collect premium (let's use $2 for this example), then buy a call at $105 to cap your possible losses.
2. The options expire and the price of the stock is $110. I have lost the maximum amount. I sold a call and collected premium of $2, and bought a call at $105, so my total maximum loss was the difference ($3).
3. Robinhood will settle these assignment after hours, and will for whatever reason show the balance as if you hadn't bought the $105 call protection. So my balance may show a massive loss until the reconcile both the short and the long end of the calls.
I have seen my balance go to -200k before when it was way in the positive before the day ended. This happened to be a Friday and it wasn't resolved until the markets opened the following Monday.
Luckily, I realized what was going on, but many novice investors may not.