So I am trying to figure out what happened with my filenames. In this particular folder they were _MG_0917.CR2, _MG_918.CR2, etc. Now they are _MG_0917-2.CR2, _MG_918-2.CR2 and so on.
Under what circumstances does the "-2" get added? — (No, I didn't do any renaming btw)...
"-2" generally gets added to file names when you import duplicates with the same file names.
I would suggest you to do a search for file name "_MG_0917" in Lightroom and see if it shows only one image or both with and without "-2"