OK, I might have been a bit hasty on this one. I powered the slug down using the power button, shut down the disk, then powered everything back up again.
It’s now run for over 14 minutes (much longer than the last 4 times I started it) and is just about to (hopefully) serve up it’s third song………… yes, it did.
So there was a problem, but a minor one it seems.
Forget I said anything.