B&O products are known to have issues with mesh networks, or even with standard WiFi hotspots sharing the same SSID.

In the latest B&O products update, a  new undocumented "WiFi" setting for roaming has been introduced that may fix mesh network issues, worth trying it even if it is not obvious that it is related to this issue. Not sure if the BS 35 was updated though.

The most common problems from Sonos owners, which are also applicable to B&O, are that (1) all the speakers & players must be "on the same subnet" and (2) "all types of broadcast packets get passed thru".  To me, it sounds like you do not have problem (1).  Solving (2) is harder, but for *some* mesh systems delving into the various configuration menus, looking for words like "re-broadcast", "extend", & "pass-thru" in front of capitalized-letter acronyms and "-packets", might help. [Edit1: Re: (1), some mesh systems can segment the network in software even if the IP addresses are on the same subnet, just like some (older, broken!) Wi-Fi access points segmented their 5GHz devices from their 2.4GHz ones, or the TP-Link can in "Router mode" vs. "Access Point mode".  "Guest network" is an example of a feature designed to do just that!  This gives you 3 more things to check, but because you can operate but not get sound, I doubt these things are happening to you.]

Sorry this is so general -- hope someone who actually owns a TP-Link Deco<n> system will chime in!

[Edit2: Not to hijack the thread, but can someone who knows say if B&O's network link is "run on" TCP packets which are acknowledged&verified, but the sound is inside UDP packets just "cast into the ether"?  I always thought this was how it was done, but have never run Wireshark (e.g.) to look.]