Thanks for your careful reading and inference regarding the potential causes.
If your credit balance truly didn't have any deductions, then I guess it's a wash
It's hard to know whether my Credit balance had a deduction because I'm not sure of where that balance is tracked over time. The Credits often expire and get replenished so it's hard to know for sure what my Credit balance was at that time.
I think there was/is an error somewhere in Uber's system. Part of the system believes I had Credits when the ride was taken, and another part of the system believes I didn't have Credits. This is a major red flag of a serious bug that should have escalated this issue to a high-level engineer to diagnose and remedy. Instead, eventually the issue was allegedly sent to another team, but as far as I can tell, this "other team" never looked into it.
It definitely makes me wonder how many people were similarly impacted, but didn't happen to notice.
Yeah, I imagine I can't be the only one. It's a hard error to catch, since it requires you to scrutinize your credit card charges closely. I've never encountered a situation before where a company refuses to honor the method of payment shown on the receipt.