did you ever get a resolution to your issue?
I am facing same issue.
For me I am hosting myself in AWS. Strange thing is I have 2 site and separate infrastructure and one has this issue and one does not.
I have noticed when I used the form upload with a ~50 meg file it will get to about 50% and then the browser status bar message will change from the percent complete to "resolving host" and then the percent starts over.
If I use the drag and drop method I get the same result that Francisco noted.