I didn't realize that the bag drop deadline was flexible. I was once denied at BUR after checking in online but arriving at the airport after the T-45 deadline. And I had a large bag (I was on my way back from Japan, with a few days in LA on the way back, so it was not a normal short domestic trip) so going through TSA and gate-checking was not an option.

I was offered a flight the next day (it was the last BUR-PHX flight of the day) and asked about LAX-PHX later that evening, and was rebooked on that instead. So it only cost me a BUR-LAX uber ride.