Disappearing Pulse Flex 2i speakers

My set-up is a Vault 2i with 4 Pulse Flex 2i speakers connected. Two are in the lounge (Lounge1 and Lounge2 linked as a stereo pair), two are in the kitchen (Kitchen1 and Kitchen2 linked as a stereo pair).

Today, everything seems to have stopped working. The first thing I noticed was that only Kitchen2 was showing up in the player drawer. I've had this before and the usual fix has been to turn them off, wait a few minutes and turn them on again, at which point they reappear as a stereo pair. While they were off, I noticed that only one of the lounge speakers was showing up in the player drawer. Again, this has been fixed in the past by turning off and turning on again.

I couldn't get either pair to appear so I rebooted the Vault. This didn't work so (on the basis of some previous posts) I suspected a network problem. I rebooted my router with no effect. I then suspected the wifi extended which the vault is plugged into so tried a completely different (and known to be working) extender but with no effect. The wifi signal is strong.

Some of the time, the lights on all speakers are blue, but occasionally one or other of the lounge speakers will go through the red > flashing green > blue cycle. The kitchen speakers are both blue but not showing up in the player drawer.

I think I've tried all combinations of turning off and turning on but I've now run out of ideas and can't get any music out of any of the speakers. I also don't seem to be able to achieve anything through the app.

Any suggestions much appreciated.

Cliff