Cannot Connect to QS Sessions


We have been using TeamViewerQS for a few years now and we connect to clients using the Remote Control (Windows authentication) option.

Recently we have been having issues with about half the clients, where we don't get prompted for our credentials when we click Remote Control and the status changes to "connecting" but it never connects.

On the client machine, they can see the usual connection window with the connection ID and it says something like "waiting for support to connect"

We are using the latest version of Teamviewer (15.18.5)and the clients are using the latest QS. We originally thought it might be something to do with our network or if the clients were connected via wifi instead of cable, but we have proved this isn't the case and we randomly can't connect to clients who are in the same building and connected the same way.

Clients are all running the latest version of Windows 10 Pro.

Please help!