Can't connect Pay:1 surround speakers anymore (since recent update?)

Recently I noticed that my Pay:1 surround speakers, which are connected to my Playbar, didn't work anymore, after working fine for several months.
These speakers do show a contineous white led, but don't give any sound. Also when I configure the leds to deactivate from the Sonos App, only the leds on the Playbar deactivate and those on the Pay:1's stay active.
When removing these Pay:1 speakers from the room and adding them again, they are detected, added, but in the last stage (preparing to work together) it gives a failure.
Resetting these Play:1's to factory default and adding them again gives the same result.
Resetting both the Playbar and the Play:1's and reinstalling the whole setup from scratch also gives the same result.
I checked the room for 2,4 GHz coverage (using Wifi Sitesurvey toolset) and this is more than adequate (> -60 dBm) at all speaker positions.

So what am I doing wrong, or might a recent update (8.1) be the cause of this?

Any help would be appreciated.