The two I remember are old and apparently unsolved ones. So old I don’t have a record even of my own contributions.
With the Calc spreadsheet you can’t/couldn’t protect the sheet while still allowing data entry. It might be a sales quotation or invoice issued by a micro-enterprise, where an accidental change to the layout could have nasty consequences. Perhaps less serious with a school worksheet or homework assignement, though teachers may have other things to worry about.
Here’s a link, which gives a link to the prehistory which seems to be inaccessible: Protect sheet options - English - Ask LibreOffice
The commercial offering WPS Office make use of this bug as a ‘selling point’. When I tested it a few years ago, it displayed a big self-adulatory pop-up. WPS is a bit expensive after the first year, but I liked it because it has original ways of doing things.
This sort of issue helps explain why businesses favour bespoke locked-down database applications, so (very old joke) your know-it-all boss can’t crash the company with a typing error in Excel.
…..
The other ancient bug is in fact a complete set of bugs: Libreoffice (Calc, Writer & I don’t know what else) has many difficulties with date, time and number formats. For example, the date you type isn’t always the date you get. Just one link, a recent one about dates:
The above link doesn’t mention the chaos that strikes when your document is opened in a different locale (country) that has different formatting conventions; I won’t try to describe what happens if the language is different as well.
A least in the old bug reports, the trouble was ascribed to a design fault that can’t be corrected because that would mean changing the Open Document File specifications.