Files Not Playing

[Torikichi]

As advised in the "My control point can't see MinimSever" section, I'm starting a new thread for help. I use LUMIN largely as the control point, and both the MinimServer Music Library on my Synology ds214play and the Player, Upmpdcli on an RPi 4 installed in an Okto Research dac8 Stereo DAC, are visible and selected. However, when tracks are selected, they do not play. I've tried the power off routine a number of times and switching off the 5 GHz band, but this hasn't solved the problem. Until now, the last time I'd used MinimServer was 3-4 months ago, when it was working fine. Since then, I've moved and had my BT Smart Hub 2 replaced because the original developed a fault. I was unable to try the original Hub with MinimServer before it failed. Otherwise, nothing has changed. On checking the Hub settings, both the NAS and renderer are visible. I don't know whether this is related, but I've also tried a USB connection from the NAS to the DAC using Audio Station/DS audio as the control, but this isn't working either. However, a USB connection to my computer where I've the same music files stored, works fine.
Can anyone help?
Thanks,
Paul