Unable to rename some documents in Finder

For no discernible reason, I am unable to rename certain documents in the Finder. This is the error I get...

...but as you can see, I'm not using too many characters or any "illegal" punctuation. (I have literally hundreds of files with names formatted with dashed dates, and even if I take out the dashes, I get the same error. In fact, I get the same error even if I try to name the file literally "a.pdf.")

This most often happens with Excel workbooks, and second most often happens with PDFs — and if I have an Excel workbook that cannot be renamed, and I "print" a PDF from part of that workbook, that PDF will also not be rename-able.

I tried renaming from within Get Info. No dice. I tried rebooting. No dice. I tried moving the files to a different folder and renaming them there. No dice. I tried moving them to an external drive and renaming them there. No dice. I tried taking that drive to another Mac and renaming them from that machine. No dice. I tried copying them onto that machine and renaming them. No dice.

However, right-click > Rename does work sometimes on some of the affected documents, and using the app A Better Finder Rename 8 seems to work.

And just to make it weirder, these un-rename-able appear in the wrong order when a folder is sorted by name. Today's manifestation of the problem is with several files with names that begin Rent Calculation.... All of them are at the top of a folder that is sorted alphabetically, despite every other file in that folder having names that start with earlier letters in the alphabet.

Anybody have any ideas how I can fix this?