Nope, not seeing that. Metadata (tags and fields specifically, not Cover Art or anything requiring file manipulation) is one of the most reliable parts of the Client/Server setup in MC.
I assume that you use a different Username and Password for "Authentication" and "Read-only Authentication"? Using the same in both could confuse things.
With Authentication, the first time a Client is connected after turning it on, or changing the Username or Password, MC requires the Username and Password to be re-entered, if I remember correctly. The MC Client then remembers those credentials and uses them next time the Client connects to that Server.
Try changing either or both the Authentication Username and Password on the Server to something unique, and then reconnecting the Client. It should ask for the new credentials when you do so. If not, it is connecting as Read-only. Try changing the Read-only Password and reconnecting the Client, then when it asks for credentials, enter the Authentication credentials instead of the Read-only Authentication credentials.
If all that doesn't work or is too hard, I think the setting at "Options > General > Advanced > Reset saved internet passwords" on the Client will also reset the Authentication passwords the Client has saved, forcing you to re-enter them. Then do as above. But that method will have MC forget all saved internet passwords such as "Doctor Who", podcast site, other linked internet site and so on. I think. I've never tested that fully.