That is a possible explanation, although I think it was weirder than that, because I remember checking some "obvious" settings like that afterwards. I also re-encoded the file with VLC media player out of curiosity, where it should have just re-encoded whatever audio track it had, without adjusting it to a specific output device, and the resulting file then also had the same issue when played in SMPLayer (whereas the original worked in SMPlayer).

I might still have both files laying around on my NAS, but I myself at least don't really have the energy right now to go into a rabbit hole again years after the fact, and sharing them would be non-trivial.