Can't save MS Word files anymore on my Mac

I was having the same issue with a shared document, getting the message: 'The save failed due to lack of memory or disk space.' This issue also prevented me from saving a local copy of the document. I disabled the Zotero add in, but that did not help.

Force Quitting MS Word and reopening fixed the issue. To do that on macOS, right-click the Word icon in the Dock, press and hold Option, then click Force Quit.