You can still call Sonos tech support but your statement that you have reset your ROUTERS (plural) leads me to believe you have two networks hence you are getting the warning “connect to the Internet” as your devices are most likely jumping between nodes.
You say you have a TP Link Deco mesh. I’d guess your nodes are generating IP Addresses and your device is connecting to another node. Only your main node of the TP Link Deco mesh should have DHCP capability to assign IP addresses. Also, if you are still using a router provided by your ISP it needs to be placed in Bridge mode, if you cannot turn off its Wi-Fi.
Also when wiring a Sonos speaker during setup it should be wired to the main node (router) in the mesh; not one of the extenders.
So my conclusion is that your network is not properly configured. To further clarify a misconfigured network can go undetected by other Wi-Fi devices such as your Android as it doesn’t care from where it connects to the outside. However, a misconfigured network is problematic for Sonos.