Munson IT Tech here.  I may have found a solution to this issue.  

Our instructors were reporting the same thing when it came to downloading this Semesters Student Finals.  We found that anything over the 500mb limit was getting crunched down to a lower resolution, from 4k down to near 480p video.  

After some digging I found within Course > Settings > Quotas, that our user quota was only set at 500megabytes, and our Course Quota at 2500 megabytes.  We brought our user quota's up to 2500megabytes and Course quota to 25000megabytes to ensure enough headroom for the course storage, and click Update.

We tested uploading a 1.5 gig file, and downloaded it as intended and we were able to pull a 4k file this time.  Possibly a new feature or update to Canvas could have reset these values to a default setting.  This seems to have resolved our issue without having to Zip(compress) files.  Students did have to resubmit their work however.