It often happened, with the newest updated Affinity Publisher, too.
When I move a picture from the page to another, it happens (not always!) that the software just disappears from the screen.
What was I doing? Editing text and thus repositioning pictures. Which I did not insert in a frame, but with the picture icon directly.
Hans, Germany
PS.: This seems to be the wrong place, but "Bug"-Report was deactivated.