Calc cell comments created in OpenOffice have disappeared

I just started with LibreOffice. I’m working with some old spreadsheets (originally created in Excel) that have extensive cell comments that were added in OpenOffice, and all of the comment frames are now blank. The comment indicators (red marks) and frames are there, but there is nothing in the frames, i.e., the comments themselves are gone. I’m also unable to enter new text into the existing comment frames. Some cells contain comments that were created way back with Excel 2003, and those comments are still visible and functional in LibreOffice. Is there a way I can retrieve the comments that were created with OpenOffice?