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Have you reconfigured the Sonos Mesh System? In the Sonos app (I'm on iPhone, but probably similar on Android), connect one of the Sonos speakers via ethernet to the router (temporarily for setup purposes) and go to Sonos App>More>Settings>Advanced Settings>Wireless Setup, and follow the instructions.
It's something I've had to do every time I've got a new router or made any changes to my network (recently installed BT Complete WiFi, and before that Whole Home WiFi) and had to go through the process each time.
Some further info here - https://support.sonos.com/s/article/1061?language=en_US
Also some suggestions to plug one of your Sonos devices to the router permanently, this will put devices into a Sonos mesh, rather than using BT WH, however either should work: