One individual incident does not a trend make.
Every time I've done this - adding nights to a stay - I've just gone to the app, booked a new stay for the new nights in the same category of room. Then walked down to the desk the day before the initial stay was supposed to end and said "Hi, I've had to extend my stay, so I've booked a new reservation for the extra nights. Can I just stay in the same room?" Every time the response has been "sure, stop by tomorrow to update the key cards."