Logic would say the stereo pair has been broken. Here are a few options in the order of best suggested. However the choice is yours:
- Do not factory reset the speakers
- If the speakers were set as a stereo pair and for some unknown reason they no longer function as such I suggest you run a diagnostic, make note (do not post in a reply) of the reference ID and call Sonos tech support
- If speakers still show as a stereo pair in the app I suggest removing them as a stereo pair. The speakers should revert back to separate rooms (sort of). The speaker flashing the green light may not so set it up as a room; as if you were adding a new product. If that is successful then set them up as a stereo pair again
Together Everyone Achieves More = T.E.A.M.