Google Cast Speakers Missing in Desktop App's Device List

[PilotFlying]

Device

Desktop PC

Operating System

Windows 11

My Question or Issue

In the "connect to a device" list, the (android) mobile app will show a google home speaker group along with the individual speakers it comprises. (So that you can play on e.g., either "Bedroom Nest Mini" or on "All Nest Minis").
The desktop app, however, will hide the individual speakers and present only their group in the devices list.

I deleted the speaker group, in the Google Home app, and desktop spotify listed the individual speakers. But only briefly. The next time I started spotify desktop, those google cast speakers were lost again.

Note that, sometimes, I can get the desktop app to show all devices/groups (for a while) by clearing the cache and restarting. I have "no proxy" in the network settings to be sure that the autodetect is not interfering.

Other google-cast capable devices (e.g. the TV) do show up, with the label "Google cast" in the device list.
The only way to control any of the missing speakers, from the desktop app, is to start playing on it on the mobile app (which never has a problem listing all devices/speakers). Then, the desktop app will show "Listening on [speaker missing it its own list]" and all controls from the desktop will affect that speaker.
Both the mobile and desktop apps are on the same LAN, which has a single router (local ISP-issued, VDSL, brand is "Speedport"). The PC is on wired ethernet while the mobile is on WiFi (wifi provided by aforementioned router).

There are switches on the LAN but we can safely assume these to be transparent to any app (or protocol even).

Possibly related:

https://community.spotify.com/t5/iOS-iPhone-iPad/Google-Cast-Group-and-individual-speaker/m-p/450277...