I have two Bluetooth audio transmitters which I use to transm an analog hifi system to my Sonos Era300 stereo pair. They are the generic M6 and RT-B6 transmitters. Everything used to work just fine until recently when any audio from them stopped being output by the Sonos speakers.

These days the devices still connect just fine, the connection tone plays and the blue LED lights steadily and in the app it shows the device as being connected, there's just no sound at all.

The Era300s still output audio from my mobile phones just fine when connected via BT. Also the audio from the transmitters comes through just fine when I connect them to other non-Sonos speakers. It seems to be an issue just between the audio transmitters and the Sonos speakers only.

Has anyone else had this issue recently? Any fixes known for it?