HLK testing for IoT Enterprise systems

Hi all,
I am preparing a setup for HLK testing on Windows 10 x64 IoT Enterprise LTSC.
For this I installed testbench for Windows 10 2004 on a Windows Server 2016 like for testing client systems on Windows 10 2004.
I downloaded and installed Windows 10 x64 IoT Enterprise LTSC.on a desctop computer. On this I disabled firewall for domain, public and private network.After this I installed test client from server (out of the directory HLKInstall\Client).
Now I installed my device for testing and moved the test client in a separate MachinePool in HLKManager. I created a new project in HLKStudio, selected the MachinePool and my device under test.
Up to this point all everything is as expected and known from testing on desctop operating systems.
In tab 'Tests' I see many tests. If I load now the playlist 'HLK Version 2004 CompatPlaylist x86 x64 ARM64.xml' all tests are skipped and the tab is empty.
Am I using a wrong playlist or have anyone an idea where the mistake is?