Almost always this is a player issue as mentioned. I’ve had similar issues with some files where audio just doesn’t work on one player but works fine for another. Same with subtitles. Set to an external player like VLC and see if that fixes it. (For what it’s worth, I mostly access Jellyfin from my Chromecast and I have it set to prompt me for a player each time I start watching something, one of them always works but for my files it isn’t consistent which)

Not surprised but got a source on those password claims?