Google Chrome for IOS 6 ajax file uploading progress event doesn't work
This is a known bug for Chrome on iOS, it doesn't support progress update. More details here: https://github.com/blueimp/jQuery-File-Upload/wiki/Browser-support
Also, I have reported the bug to the official bug tracker, you can see the latest updates here
UPDATE 2016: It has been fixed!
I have come across the same problem using plupload. However, it only occurred when allowing the user to select multiple files. After turning off this ability, chrome would correctly upload the files.
I have not found a solution to the problem that also allows multiple file upload.