Currently running iOS 15.2b3 on my 12 Mini and I have been having this issue since iOS 14.6; my subscription keeps randomly deactivating in my app and it is starting to get frequent. I also notice that I will have to go back into the online dashboard and clear the (sometimes duplicate) profile(s) for my 12 Mini to regain functionality. I also have a disappearing VPN profile sometimes too where the app requests a VPN profile here and there. Any help is greatly appreciated!
This is going to be fixed in the next update, it should be out in a few days.