Client does not start, when connected to USB-C-Dock

we have a problem with one Notebook (Lenovo ThinkBook 16p G2).
The Client works perfekt, when the ThinkBook ist stand-alone. When we connect the ThinkBook to the USB-C-Dock (Lenovo Lenovo 40AF0135EU), then it also goes on working.

But when we start die Thinkbook while beeing connected to the Dock, die Client does not start.
No notification, no Process in the Task-Manager, nothing. No chance to start the seafile-applet.exe.

After disconnecting the dock, seafile-applet.exe can be started.

Client ist installed at C:, Data at E:\ - both letters are static.

How can we analyse this problem?

Kind Regards