Preview stores my notes but doesn't display them on reopening

Hi there,

I'm currently annotating lab reports I got in PDF format and using Preview. As part of my workflow, I highlight some parts of text and from time to time, I add a note with comments. As recommended, I am only using Preview and don't mix software.

Unlike a previous topic where notes and highlights were lost, mine are indeed correctly stored, but the little colored square that shows a highlight also has a note simply disappeared on reopening the same file.

Here is an illustration from the Inspector: green highlight has a text note attached, but unless one is using the inspector, the note can't be read.

How can I make notes re-appear and more importantly, be reliably displayed?