When adding checked baggage to my departure flight, the app asked if I wanted to add the same to my return flight. I said yes, and it reflected on my booking details. I confirmed this several times because I didn't want to be charged a higher fee at the airport. I got to the airport and suddenly it's not in my booking and the desk agent didn't see it either. And I had to go online, not the app, to re-add the bag. Useless and frustrating, just like Customer Service.

The way the app is set up for check-in there are constant nags to upgrade. there's also a place where it looks like you have no choice but to apply for a credit card to continue. Way too many attempts to grab more money. Every move on the app generates a prompt for an "upgrade", or add on and then the confirmation that you don't want it followed by another confirmation asking if you're sure.

Missed my flight because the app failed to issue a boarding pass and there was almost no help. I reinstalled and restarted the app - still nothing. A rep blamed me for being late, claiming I didn't hit the check-in button in time, even though I did. After rebooking (Frontier even tried to make me pay the fare difference), I still couldn’t get the boarding QR for the next flight more than 12 hrs prior - thankfully it finally worked on an iPad. Just terrible!