Two near identical setups; one works, other doesn't

[nickc]

I'm baffled on two fronts:

1. Several weeks ago my aged QNAP TS-109 finally, partially, gave up the ghost. I can still access its samba shares on the network, but I can no longer log into the admin web interface and after a power restart I lost touch with the MinimServer+MinimStreamer app which had been happily running for months on end: its icon was no longer shown by MinimWatch on my linux desktop, it wasn't showing in BubbleUPnP or Volumio and without the admin interface I couldn't get to see the status of the MS app from within the TS-109. Then yesterday when I booted up my desktop suddenly the MS icon appeared again, nice and green, and I'm listening to BBC radio from it at this moment, rendered by Volumio on a Raspberry Pi. We did have a brief power cut yesterday, but we had a much longer one a fortnight ago and I've powered the TS-109 down and up again several times since it went down in hope of getting the admin interface back. I'm still without that access, but out of the blue MinimServer seems to have resurrected itself - I'm more than ever in awe of this amazing software!

2. Being back in touch with MinimServer I've been able to investigate the second thing that baffled me. I have another instance of MinimServer+MinimStreamer on a much more up-to-date QNAP HS-251+ in another room, so when the apps on the TS_109 went down I switched to that, or tried to, but found it wouldn't play my radio stream of choice, even though it had been fine the last time I used it (much less frequently for streaming on that setup) following help from Simon to get its settings right for play by Volumio. Being short of time at that point I resorted to using Volumio's own web radio sources rather than embark on further troubleshooting on Volumio and/or MinimServer. With the TS-109 setup now accessible, this morning I checked the system properties on both servers and changed the settings on the HS-251+ to match the TS-109 (a matter only of removing ffmpeg from the stream.converter field and *:wav from stream.transcode) but as I anticipated, this didn't resolve the problem. Next I checked the two playlists; they are identical: eg #EXTINF:-1,[R3;aac,48000] BBC Radio 3
http://a.files.bbci.co.uk/media/live/man..._three.mpd
Finally I checked the MinimServer log for each NAS. The last entry on the TS-109 (where streaming is working) is "MinimServer[QNAP-TS-109] is running". On the HS-251+ it is
"MinimServer[LandroNAP] is running
MinimStreamer: transcoding converter is 'ffmpeg'
MinimStreamer: no transcode setting is configured
MPEG-DASH: Buffer length exceeded: http://time.akamai.com/?iso
MPEG-DASH: Buffer length exceeded: http://time.akamai.com/?iso
MPEG-DASH: Buffer length exceeded: http://time.akamai.com/?iso
MPEG-DASH: Buffer length exceeded: http://time.akamai.com/?iso
MPEG-DASH: Buffer length exceeded: http://time.akamai.com/?iso
MPEG-DASH: Buffer length exceeded: http://time.akamai.com/?iso"
This alerted me to the fact that ffmpeg has reappeared in the stream.converter field, which reminded me of reading that MS will automatically search the system it's on to find a converter app, so presumably there's no way it's presence or absence would be causing my problem. (If anything, I'd expect its absence on the TS-109 to cause an issue.)
Volumio has an annoying habit of popping up error messages which then disappear before I get a chance to read them, but I did eventually catch this after repeated failed attempts to play from the HS-251+:
"Error
Failed to decode http://192.168.1.63:9790/minimstreamer/*...tream.aac; CURL failed: The requested URL returned error: 500 Internal Server Error"

So here I have what appear two identical setups of MinimServer/MinimStreamer on different QNAP NASs, one of which (on the older NAS!) plays fine through Volumio, the other of which doesn't. I'm flummoxed.