Frustrating volume level issues when listening to audio through wireless headphones

This is a bit of a strange one that I've not heard anybody else mention experiencing the same or something similar. But, as it's now been driving me crazy for a few months, I figure that I should share here just in case there is in fact somebody else experiencing the same.

The issue is that when listening to audio through any of my wireless headphones, the volume level of the audio will often be lower than it should be.

Specifically, although the volume level may be set at 40%, the level I hear is actually at about what you would expect if it were 20%.

I am seeing this behavior across multiple apps and types of audio - music in the native Music app, podcasts in Overcast, ebooks in Voice Dream Reader, and streaming radio in Broadcast to name just a selection.

I am seeing the behavior on three different sets and types of AirPods, along with a set of AfterShokz.

I have forgotten and reset most of the headphones, all with no effect.

This behavior has now been present for three iOS versions.

The volume of VoiceOver itself is not seeing this behavior. It's always where it should be.

The low audio volume isn't always present. Sometimes it just works as expected, but there appears to be no pattern to this.

If it is going to be present, it will be there as soon as I start playback.

It will continue to be low after I lock my iPhone.

Sometimes simply waking my iPhone will be enough to correct the behavior, and for the audio volume level to increase to where it should be.

Sometimes it will resolve itself if I wake the iPhone and then press the volume buttons on the iPhone.

Sometimes I simply need to wait, and after anything up to 20 minutes later the volume level will spontaneously increase.

One thing that is consistent, is that the volume level is corrected immediately if I toggle VoiceOver off. However, if I then toggle VoiceOver back on again, the volume level of the audio will often decrease.

I typically listen to audio for 6-8 hours daily, and have now got in to the routine of having VoiceOver turned off, only toggling it on when I need to do something on the iPhone. This is simply a better user experience than having VoiceOver and audio at different volume levels.

And, yes, I do know that VoiceOver and audio volume levels can be set independently, but this does not appear to be a factor here.

I did wonder if this issue might be connected with audio ducking. It didn't seem likely, as this shouldn't interfere with audio levels when the iPhone is locked and VoiceOver doing nothing. However, I did check, and disabling audio ducking did not make a difference.

I have yet to experience this issue when playing audio through the iPhone speaker. So, it does seem to be specific to headphones. I don't have any wired headphones to hand, so haven't been able to check if the issue is present when using these or is specific to wireless headphones.

So, by any slim chance, has anybody else experience this? Or, perhaps even better, does anybody have any suggestions as to a possible cause and solution?