Whiteboard turns black or white

I have a problem with Zoom since about two weeks. When I use the whiteboard on an iPad Pro it turns black or white in large areas after a while so that I have to stop the session. The content underneath is still visible for other users in the meeting, but I cannot see what I am writing any more.

I tried reinstalling the app, even set back the entire iPad and also contacted the Zoom support via the chat, however none of this helped.

Has anyone got an idea or experienced a similar issue? Otherwise I have to cancel my pro-account because Zoom has become useless like that.