Frank there are a couple of issues.
And yes, the version of iOS can impact performance since the app has to connect thru the OS to get to the internet/wan/lan etc…
Also the latest official release that’s been pushed out is iOS 18.7 (I just checked and am updating now…)
Having tracks not available… ok … is this on your own storage within the device? Or are you using a streaming service like Spotify.
I can tell you that if you don’t download a track, its very possible that the track is no longer available.
This can happen for a couple of reasons… e.g. there’s an internal storage problem… or they pulled the track for a couple of reasons…
A separate issue of not being able to see the device.