I seem to recall that these particular routers require the user to enable IGMP Snooping (not enabled by default on some TP-Link models). Settings —> Advanced —> Network —> IPTV and enable ‘IGMP Snooping’.  

See if that is perhaps the case with your router configuration and maybe see if that resolves your issue.

Already tried that and unfortunately it does not fix the issue.  

As you have a new router then perhaps see this link for the steps to add the new WiFi network credentials to the Beam:

https://support.sonos.com/s/article/1061

Also, after a change of router it is essential to power cycle absolutely every device on the network.

I’ve been beating my brain on this since yesterday. I have the AX73 router. I got it to work by disabling AP Isolation. I believe you go to Wireless → Additional Settings → Toggle AP Isolation to unchecked then Save. My sub and One SL showed up. Good luck and hopefully other’s will find this solution.