So, have you tried, at least temporarily, wiring one of your two Sonos One SLs to your router with an Ethernet cable? Or tried changing your WiFi channel on your router? Some of which you describe might be simple wifi interference , depending on what the CS person said, they have access to data from your system we don’t., which makes guessing, given the lack of information provided, all that more challenging.
Thanks for the reply Airgetllam. I’ll try your suggestions to see if that cures the problem