Screensharing does not work on private calls

Hi folks,

i use msteams for teaching.

During the hole last term (from april to june) it was possible to see a shared screen of a student into a private call. Since some weeks i only see a black background with the studentlogo in this situation.

If the student use screensharing into a meeting on a canel it works fine (but all other members of this meeting could see the screen too).

Is there any idea to solve this?

Thanks in advance to any hint.

Ralf