Thank you both for the quick replies. So of course a few minutes after I gave up and posted here the file opened and I was able to make changes and export again. I closed and re-opened the file and it seems to be working, it just takes a long time to open.
As far as the proxy issue, I had made sure to turn off proxy before exporting but the proxy files were still included in the export. I was able to fix it by opening the .mlt in notepad and replacing the proxy file locations with the location of the converted full resolution files, as mentioned on the forum here: Shotcut renders with Proxies instead of original files (FIX & question)
Thank you again for your help. Sorry to bother you.