Solved.
After removing all x-rite applications and a new installation of LS, all is fine!

NB: The driver is still the same (i1_x64.sys V2.40.0.1315). It's coming with x-rite SW as well as with LS. I guess, the question mark in the device manager i1Pro symbol says only, it's not digitally signed, if I'm right.
Steve, one suggestion for the manual:
If pressing the
Change Probe button, LS opens a 10s window (timeslot) for disconnecting the probe from the USB.
If you don't do this within the10s, LS will automatically reconnect it as working probe.
If you disconnect the probe from USB after this 10s, LS does crash.
An other question:
At the moment in LightSpace I can't choose between i1Pro2 / i1Display Pro, if both probes are connected the same time at USB. In this situation LS does always connect only the i1D3, even if I press the
Change Probe button many times.
Any chance to get it realized, to display kind of a selection window about the physically connected probes, when pressing the
Change Probe button?