Qobuz won't stream to my system anymore

[Rugby (aka Daniel or Big Dan)]

That seems to be the issue. In the same thread that you linked, the OP of that thread was able to set things right by doing the following.

@AceRimmer

Have you tried logging out of Qobuz inside Roon in the services section of settings?
Then reboot the Roon Core.
Then try logging back into Qobuz again inside Roon.

Has helped myself in the past to clear up odd Qobuz behavior.