Apple volume turned down when using headphones

For some reason, Apple have decided to let my phone analyse how I’m using headphones when listening to music, and then unexpectedly turning down the volume without even asking me. I can turn up the volume again, but this is extremely annoying.

I find this a problem because:-

this was not mentioned in the notes of what the update would include;

I listen to very varied music, so it can go from very loud to very quiet, so this makes the quiet bits too quiet to hear;

notifications come up every time it does this, with a sound that also interrupts the music;

if I am in a loud environment, the music is turned down too low to hear properly;

there does not seem to be any way of stopping this that I have found.

Does anyone know a way of stopping this. It is exceptionally annoying, and I have had to start reusing an old iPhone just to play my music through my headphones. This will not be updated as I know that this would happen again.

[Re-Titled by Moderator]