Failed to upload file Error [Object, Object] - In device portal

This is a very strange problem, when I am trying to upload the file to HoloLens through device portal, I get this error. I searched this forum and found out that for some people it is happening in Edge browser, for others in Firefox. For me unfortunately it is happening in all browsers (Edge, Chrome, Firefox)
I can rename the file, save the file, also delete the file, but cannot upload a file! This is driving me crazy, because it is important for scenario to upload a configuration file to the local storage. From which the application reads settings.
I tried running Fiddler in the background and found out that I am getting HTTP 429 response, citing too many request!