I suspect it is very rare but it can happen if there is a clinical emergency, a catastrophic event in one's research environment, or a personal/family emergency that can't wait 30 minutes and where a back-up interviewer can't be located on very short notice. While it is aggravating to have to go back another day (not virtual? are you at least in the area?), have some empathy for the interviewer who, in all likelihood, is having a much worse day than you are.