A dangling shortcut is a shortcut in your google drive that doesn't point to anything. They look like this in the google drive web page (note the trashcan icon and the "Remove shortcut" text)
As for which file, search for "dangling shortcut" in the log and you'll see. (I don't think you posted that section).
I suggest you find the dangling shortcut and fix it or delete it, then the sync will run without errors.