Strange behaviour of the selection menu (missing or not complete)

Hello,

in Rhino 6 the selection menu is not working properly:

  • sometimes it does not appear, when clicking on overlapping objects. Then, one object is selected and I can not choose which one.
  • sometimes the selection menu appears, but some objects are missing in the list.
  • sometimes it appears and works as is should.

There are some issues posted on this forum but they all seem to be not entirely similar.