We have identified a bug with the metronome on some devices running under iOS 14.2: the app may crash a few seconds after turning on the metronome.
This is due to a bug introduced by Apple in iOS 14.2, impacting several other Apps using Audio/MIDI. In order to prevent this crash, we advise not to update to iOS 14.2 if possible.
Apple have fixed the bug in the beta version of iOS 14.3. The public version of iOS 14.3 should be released soon, but if you cannot wait until then, you may install the beta version by signing up to Apple's beta program.
Sorry for this inconvenience, and do reach out for assistance if needed,
Marin from Newzik