Cannot see any notes in impress presenter view

I cannot see any notes in impress presenter view or at least this happens randomly: this happens both with ppt or odp format files; LibreOffice

I have presentations with notes and when starting the presentation mode with 2 monitors I see a random behaviour sometimes notes are present other times (most) do not appear in presenter view: the notes window is there but it’s empty.

I have tried to remove existing note and copying them back but it seemed to work for a time, then again the notes disappeared from the presenter view.

Can you help? am I missing some config detail?