I've had issues since switching to BT, though there were occasional issues with Virgin previously.
I have a grouped 5 and 1 with no Bridge or extenders, wirelessly connected to the Smart Hub. The hub's bands have different SSIDs. Regularly, and it always seems to.be overnight, the 2 units become ungrouped. Also, if I try to play the Sonos 5 using the play button on the unit, the orange light flashes and it doesn't resume. When i use an android controller, it takes a few seconds to find the system, then works as usual.
Once or twice though, the controller's have failed to find the Sonos players but rebooting my Smart Hub has fixed this.
Any ideas¿ Static IP addresses maybe?
Not sure why this always seems to be at night, I don't think my router is powering down to save energy in its settings.