As usual with cloud/web app/server based software, goog sheets has shown more & more problems over time.  The biggest problem for PDF merge is the authentication glitches.

Noted if it prompts for a login during a resync, it logs in successfully but fails to update any values.  You have to resync again.  It hasn't been easy to test since there's no easy way to make the login expire.

Other than that, goog sheets doesn't allow entering multiple lines in a cell.  Openoffice allows entering multiple lines with ctrl-enter.  Multiple lines in goog sheets can be fenegled by pasting all the lines at once.  Then the problem becomes selecting or editing multiple lines, which entails copying the entire cell into another text editor.

Browser based text editing has always sucked a bag of dicks.  PDFMerge & goog sheets both suffer in their text boxes.  Writing a spreadsheet program from scratch would be a big deal.  It's hard to imagine something as platform independent as the current system being any less bug ridden.  If it was just for Linux using scratch X11 calls, it would be solid.  These glitches are why bare X11 programs continue to persist.  The API is just abstracted enough to be more effective than a framework for a lot of tasks but just primitive enough to make a full GUI extremely laborious.