I sent those questions, and I do not have a solution.
I was told the max file size is 50 GB. The file I'm trying to upload is 26 GB which is well under the max. My internet is 1.5 GB download and one gb upload. I'm the only one on the internet at the time of failed upload. Also, it is a single file. So none of those issues you mention seem to fit the description of my problem.
When first contacting support, I sent them a screenshot of the console log showing various errors appearing. The file type I am trying to upload is.MXF, which I have uploaded multiple times before successfully.
I use this for work to share files with my employees, so it is crucial we get this working, or I am going to have to look for a new solution that is more reliable.
(this email I sent May 27 today, May 30, and I do not have the answer)