When I filter on my stories on the active sprint board, not all of the stories assigned to me for that sprint appear on the board. If I search for the story that I know to be missing from the board, it is found and displayed. When I return to the sprint board, there it is. However, other stories have now disappeared from the sprint board. If I search for a story that has disappeared, it will then reappear on the sprint board, but now the other story is missing again ... and around and around.
This has been going on for months now, e.g.
Here is my sprint board. I know another story is active in this sprint but is not showing.

When I search for that story, it is found. Then when I return to the sprint board, there it is. However, the others have disappeared.

If I search for one of the newly missing stories and then return to the sprint board, those stories reappear, but the third story goes missing again, and around and around.