So, after further troubleshooting a narrowed it down to a faulty Playbase. It looks like the WiFi is not working anymore on that device. I reset everything and added each speaker back one by one, leaving the Playbase last. All 3 speakers and the sub i could add without any problem. The Playbase though does not create the "SONOS" WiFi network when adding it. I could only add it using a network cable. So i setup 2 rooms, Livingroom and Livinroom2. One "room" has the Playbase and one has the 2xPlayOne and the Sub. All speaker work fine i can even group the 2 "rooms". What doesn't work is to add the sub or the 2PlayOne to the Playbase as surround speaker. It always fails with an error. So i think the Wifi module is either broken or the software update "disabled" the functionality. Looking forward for support getting back to me.