Issues with Version 3.702 on Raspberry Pi

I have 3 Raspberry Pis running Volumio around my house. Generally the system is fantastic and I play either Internet radio or music direct from my NAS via MiniDLNA server running on another dedicated Raspberry Pi.

All cabled connections are Gigabit over CAT6, wifi is provided by Ubiquiti pro APS with a controller.

One device was upgraded to 3.702 a couple of weeks ago. It’s a wired device, so no wifi (and connected to the same switch as the DLNA server and the NAS). Since the upgrade on some albums it simply stops playing. The interface (iPhone / iPad app) show no progress and loses the track info (i.e. the title of the track)

mpd.log shows the following when the error last happened:

Jul 20 15:41 : player: played "http://192.168.70.53:8200/MediaItems/235247.flac"
Jul 20 15:47 : alsa_output: Decoder is too slow; playing silence to avoid xrun
Jul 20 15:47 : player: played "http://192.168.70.53:8200/MediaItems/235248.flac"
Jul 20 15:47 : exception: Bad song index
Jul 20 16:00 : exception: No such playlist

FWIW I’m not creating play lists on the Volumio, just playing albums as listed on the NDLA server. The database of which gets updated pretty regularly as I add new music.
Any suggestions?

TIA

C