Sorry for the bump--but I still have this issue, and turned on logging on the foobar upnp plugin, it's giving this event when the song reaches 5:20:
[00:29:49] foo_upnp: 245.245519: upnp_server_conf::get_profile(943)/4868: INFO: using default profile (User-Agent:foobar2000-mobile/1.x)
[00:29:49] foo_upnp: opened 'file://G:\Music\ALL\Kikuo\Kikuo - Kikuo Miku 6 (2019)\Kikuo - Kikuo Miku 6 - 02 あなぐらぐらし - Hole Dwelling.mp3' for streaming, profile: Default, MP3 / CBR 320 kbps, replaygain: on, DSP chain: off
[00:32:29] foo_upnp: submitted statistics for 'file://G:\Music\ALL\Kikuo\Kikuo - Kikuo Miku 6 (2019)\Kikuo - Kikuo Miku 6 - 02 あなぐらぐらし - Hole Dwelling.mp3'
[00:35:08] foo_upnp: 564.564660: FbMediaServer::CheckAuthentication(401)/27072: INFO: received LAN request: http://192.168.86.129:56923/content/ee5cc7c0ffe330148111f5ba51fc1bda.mp3?profile_id=0&convert=mp3 (User-Agent: foobar2000-mobile/1.x)
[00:35:08] foo_upnp: 564.564661: PLT_HttpHelper::ToLog(432)/27072: INFO: FbMediaServer::ProcessFileRequest
GET /content/ee5cc7c0ffe330148111f5ba51fc1bda.mp3?profile_id=0&convert=mp3 HTTP/1.1
Host: 192.168.86.129:56923
Connection: close
User-Agent: foobar2000-mobile/1.x
Accept: */*
Icy-MetaData: 1
[00:35:08] foo_upnp: 564.564721: upnp_server_conf::get_profile(943)/27072: INFO: using default profile (User-Agent:foobar2000-mobile/1.x)
[00:35:08] foo_upnp: opened 'file://G:\Music\ALL\Kikuo\Kikuo - Kikuo Miku 6 (2019)\Kikuo - Kikuo Miku 6 - 02 あなぐらぐらし - Hole Dwelling.mp3' for streaming, profile: Default, MP3 / CBR 320 kbps, replaygain: on, DSP chain: off
After this the song starts over.
I don't know for sure if the error lies in foobar mobile, foo_upnp, or in my network configuration somehow, however--no other UPnP players do this behavior. I really love using foobar mobile, and there really isn't a good alternative music player on Android, from what I've seen. I hope this can be resolved (it's possible there is something wrong on my end, but like I said, VLC and other uPnP players on android don't have this issue).