SOLVED: Raspberry Pi Zero 2 and FLAC files

[TheDreadPirate]

Does this issue happen while you are on LAN as well? Or only remotely?

And just for clarification, you've manually port forwarded but "Automatic port mapping" is still disabled, correct? That uses uPnP to create a port forwarding rule, but those automatic rules expire. I've seen users who both manually port forwarded, but left on automatic port mapping, have issues where the uPnP rule overrode their manually created rule and then expire.

Are you also able to check if your server has run out of memory or swap?