I keep trying to download my video as an MP4 and all I get is this

I've tried every kind of troubleshooting mentioned in this forum (deleting cache/cookies, using a different browser, using incognito mode, deleting parts of the video to see what the issue could be. I've even tried just pulling a template and trying to download that without editing anything and I still get this message.) I am hoping for a fix for this so I can start downloading my projects. Help! The only animated thing I was able to download successfully is an animated character voiced with a background--but as soon as I try to drop that into a project, I get the error.