Can't edit a note - a line appears

DavidC360  - I'd been having this same issue.  I was finally able to resolve it by:

1 - unhiding all rows/columns

2 - right click on the cell with the note and select "Edit Note"

3 - follow the line to the note box and click/drag on one of the edges to make it bigger.  For me - all the note boxes were at the top of the spreadsheet and the note boxes had been collapsed so all I could see was the six little squares that form the outline of the note box.

4 - when big enough to read it. click/drag on the note box again and move it closer to the cell that the note applies to

I am guessing MSFT screwed something up with a recent upgrade and our notes boxes were all minimized and moved to the top of the spreadsheet.  Good luck.  Hope this helps.