I've got many notes (the yellow non-threaded formerly called comments) in my excel sheets. Since the latest software update I can not display/view my notes anymore.
The cells containing note still show the red triangle-mark, but the note does not show up when I mouse over. By clicking "show all notes" in the ribbon menu, it will just only show the connection lines between cell and invisible note rectangle. But I can not access view or even edit the notes.
Also right click on the cell -> edit note does not show anything.
I have same issue. It looks like MS was nudging users off the old yellow notes feature (which I use a LOT) toward the "comments" side-bar approach. I hate it when developers get a "good idea" and force us to change, especially with no notice or transition support. This is a HUGE pain. But, will MS notice? I doubt it.
I have had this problem too. What I found worked was to copy the cell to a new tab. The Note will show up there (though I had to move the frame buttons to make the square visible). Then I copied the cell back to the original tab. This fixed the issue for me. Hope this helps.