Fotomagico 5 : blue vertical lines in story board

L.S.
I am using Fotomagico Pro 5.6.14 on a new Macbook Air with Apple M3 processor running MacOS 15.3.
Thin vertical blue lines appear in the storyboard when I move the slider.
I know Fotomagico 5 is no longer supported, but maybe some one knows whether this is a known issue?
I still have Fotomagico 4.6.9 which seems to work works fine on the new Macbook, so I’m afraid I have to return to Fotomagico 4.

Geert.