Ok. It was a font issue. I had done a search for "free monospace fonts" and I got the original file from some random free font website. It must have been old. I went to the link you provided to the Google font and downloaded that. I uninstalled the old one and installed the new one, and it seems fine now. Still and odd issue though, because, as you mention, ligatures and monospace fonts don't seem to make much sense.