Upload not working when you are uploading larger packages. Or shows up strange percentage values, like at full progress bar it shows 1.3% or 0.1% . This is a server issue.
Your server is not accepting Patch requests, consult web host to enable Patch request in server. When you upload big files, bigger than the upload limit, VibeBP uploader breaks it down into parts to upload.
The second and subsequent requests are called Patch requests as they add up to the same file. Sometimes servers are not configured for that and they show strange 406 errors.