Hello @MarthaIrvine
Which method are the students using to upload/record these videos? Is there a specific format or is it more of a free for all? There is the canvas media recorder that the students can use by default, but anything more than a few minutes should be recorded elsewhere in case there are browser, device, internet issues that can cause the videos not to come through. There is also Studio or Kaltura that many schools use - by chance one of those? Or do the students get to upload any format of video that they want?
Because of the complexity of the issue, and the concerns for privacy, it would be best if you contacted Canvas Support directly to pinpoint the source of the issue and provide a resolution:
https://community.canvaslms.com/t5/Canvas-Basics-Guide/How-do-I-contact-Canvas-Support/ta-p/389767