Sorry my solution post did not go through, here it is for the record:
I have been testing all day trying different variations and I finally got the CC button to work on our Pathlore LMS. I was using WEBVTT for the CC which I had read is recommended for use in Lectora. I tried using XML instead and it worked immediately. Thanks mraines for your suggestion, SRT would not work on mraines LMS but VTT did, and for me VTT did not work but XML did. I guess the takeaway is LMS’s don’t like certain files for Closed Caption – try until you find one that works.