Headphone [and Bluetooth] audio is broken on PinePhone Pro: playback is routinely stopped

This is a strange issue I've been running into lately, and I am unable to pin down the cause.

First, the issue seems not to affect the built-in speaker, but only using the headphone jack or a Bluetooth sink.

Also, I am basically only able to reproduce the issue in my vehicle, whether driving or not (engine on, but also not); and pretty much never when stationary at my home (though when using the Bluetooth device, a similar issue seems to present; I suspect this is the fault of the Bluetooth device as others seem to not present it in this scenario).

The issue presents even with the cellular modem disabled (even after systemctl stop eg25-manager), and also with the Bluetooth and WiFi radios disabled (as via Phosh / GNOME settings).

The issue: when playing audio (locally stored on the device, but also otherwise), Totem (and other apps, like https://github.com/xou816/spot) will routinely stop playing and must be resumed by pressing play again. For Totem, playback resumes immediately; waiting or changing any settings is not required. Playback will pause again sometimes in mere seconds (or less), and other times after minutes, though playing back an entire 3+ minute track without interruption is basically impossible.

I am out of ideas for how to diagnose this; especially frustrating is that it only seems to present in my vehicle: I haven't tried other vehicles or environments yet.

What could be causing this? What kind of logs should I capture to help diagnose the problem?