‘we can’t connect to Sonos’

Recently I am repeatedly getting the cannot find your Sonas system. I follow the instructions to press a button on the nearest speaker, the app says connected, I press done and it returns to ‘cannot find your system’ message! I have not changed my router, I have tried turning it off and on again and whilst this restores the connection, it quickly drops out again. I have 2 x 3’s, 2x 1’s and a Play, none of them are hardwired and have always worked perfectly. I use an iPhone and an iPad as controller. 
Any ideas, anyone?