Sonos does not support networks with extenders. That doesn’t mean it won’t work, but that it is often problematic, even if ir is down to suboptimal setup. I think @AjTrek1 is very likely to have identified the problem. Make sure your extender is is “bridgw” or “access point” mode - simply using the same network credentials is not sufficient.
You would probably improve the stability of your system by wiring one speaker so as to trigger SonosNet. Do you currently have a wired Sonos device? That would change my answer.
Btw, there was no need to factory reset anything. You just needed to temporarily wire one speaker so as to add the new network credentials.to Sonos Or amend the network credentials to match those of your previous ISP - that saves all the effort changing these details on all your network clients, not just Sonos.