My son uses two Play:5 gen 1’s which use his routers 2.4Ghz band, rather than SonosNet and I have set his router to use a non-overlapping WiFi channel (channel 1 in his case, but you can use ch 1, 6 or 11).
He has an ISP-provided router (Virgin Media-1GB monthly) and it allows a user to configure the channel-width. So I’ve set it to 20Mhz only for him, rather than the 20/40Mhz default setting, in order to reduce interference and that’s working fine for him and his family. They use the Spotify ‘family’ subscription service and do not have any issues.
They also have a Sonos S2 system setup aswell and that’s not been an issue either with Spotify, but that’s by the by.
So, if not tried already, maybe try these mentioned WiFi changes and see if it makes a difference.
If using SonosNet still go onto do the above, but set the SonosNet channel in the Sonos App network settings to a completely different channel. Also reboot your router and speakers and then let things settle for 20 minutes before testing.
Hope that works for you.