Disallow Multiple Connections doesn't work

Hello Devolutions Support,

I want to use the Multiple Connections Feature for RDP Sessions. There should be only one session at one time. The next user who tries to open should get an warning message.

In my evaluation environment everything works as it should. In my new (almost) production environment I don't get the warning message.

I can reproduce this with two users who accessing the same repository. In the options the setting "Allow multiple connections" is set to "False" for both users. For testing purposes I also set the option in the properties of the RDP connection. I've attached you screenshots of the settings. Both users don't have admin permissions.

What's wrong here?