As above, may have been doing a 'burn cycle' or you may have caught it out. My new
Cupra has hanged onto a gear for too long once early morning but a lift off of the pedal sorted it out. Its a computer at the end of the day, they still make mistakes and have thinking moments!
Do you have shift levers? maybe you knocked one by accident? Again done that before when enthusiastically driving and wondered why the gear wasn't changing.
Unless its constantly doing it, i wouldn't presume there is an issue, maybe next time shift it up manually and see if it carries on happy in that gear?