Loss Sonos Connection

I have 3 Sonos S1, sound bar, sub and Alexa S1 and they can not be found by the app. The Alexa App shows them as being there but offline. The Alexa, sub and Soundbar all work as controlled from voice or TV but they can not be found by the app. I have tried reconnecting everything but they can’t be found. I am yet to try factory reset and then seeing if I can set the whole thing up from scratch, as I shouldn’t surely need to do this? Any suggestions please?