I have an iPhone X running iOS 12.1.1. The Bluetooth has stopped working on certain apps. It works fine on apps like Music and Spotify, that is, I play a song, minimise the app, and the song keeps coming through my Bose QC35 headphones. For apps like Timer+ and timer., the alarm bell will ring through the headphones while the app is in the foreground, but it doesn’t ring at all when the app is in the background, either through the headphones or through the phone’s speaker. What is wrong? The firmware on the headphones is up to date. The OS on the phone is the latest version. I have tried deleting and reinstalling the apps. It makes no difference. This used to work, I’m not sure exactly when it stopped, it was in the last three weeks, possibly it is the upgrade to iOS 12, but I cannot be sure of that.