Cannot open an existing score

I've started a score of a symphonic piece this morning as an MuseCore 4 exercise for me. The piece is already engraved in Lilypond but I wanted to check the capability of MuseCore. Although the user interface is completely new to me and gave me a bunch of grey hair, it worked ok albeit with a very slow progress. The piece is stored locally on my computer.
When I wanted to continue with the piece this afternoon, I cannot open it anymore. In fact, the score is visible under Home/Scores but when I click it, MuseScore is "killed" without any error message whatsoever. The same happens when I doubleclick the stored file. MuseScore then starts but after a few seconds, it just disappears. The file in question is attached.