TromboneChat

I use a metronome app on my IPhone 11, via Bluetooth to a speaker. When I stop the metronome very often music is played from my music app on the iPhone, without anything else happening. The tracks that cut in have been stopped, not paused, when I’d played the previously. Sometimes they are tracks I haven’t played recently. I have not found a way to stop this.
My fairly recent iPad, that I use with Forscore to read my charts is also connected to the same Bluetooth receiver and speaker. I’m not even sure that’s relevant as the iPhone is the offender here. Any idea how I stop the music cutting in when the metronome is stopped?.
All suggestions welcome.

Close the music app before you start the metronome.