Running UI tests from team foundation server 2018

I created some UI tests with TestComplete using integration into VS to run them as VS test items.

With TFS2015, I did install a VSO agent on a physical server, which started in interactive mode (not as a service) on reboot. My build contained the "Visual Studio Test Agent Deployment" step followed by a "Run Functional Tests" step. Everything was fine.

With TFS2018, it's a slightly different VSTS agent, and I want to use the "Visual Studio Test" step. Everything is fine and the tests run as long as I have open desktop connection to the server. However if I reboot the server, and the agent starts on reboot, my tests fail with "Unable to initialize TestComplete" due to the need for an interactive workstation.

So I just can't find a way to run the tests from TFS2018 the way they ran from TFS2015.

Edit: I already tried starting a batch file as Administrator containing
%windir%\System32\tscon.exe XY /dest:console
XY being the ID of my current Remote Desktop session,.

When I run the tests from VS and than execute this batch file, the tests continue and UI objects are available. However the build steps fails with the same message.

Thanks in advance, Florian