I'm also having this issue minus the error message. I've tried uploading through Safari, Chrome on my Mac and Jamf Admin. I've also tried uploading using a W10 using Chrome all attempts fail. Jamf Admin gives an error 504. My users are also having issues installing currently uploaded packages from Self Service as well which may be a coincidence. This is all on Cloud.
I am having this same issue. Unable to upload a 22 MB file. It stops at 100% and never successfully completes the upload. A test of the connection to the Jamf Cloud Distribution point returned an Error (!), but no messaging. Now I simply get the message "Unable to communicate with JAMF Cloud". Has anyone found a resolution for this?