We are facing this issue again for Drupal version 6.37. We do not have jquery update module installed.
In our case the progress bar just hangs but the functionality is accomplished.The Drupal core and modules do get updated. When we run the update.php since ours is a https site, we get the Mixed content error
Mixed Content: The page at 'https://example.com/update.php?op=start&id=14' was loaded over HTTPS, but requested an insecure XMLHttpRequest endpoint 'http://example.com/update.php?id=14&op=do'. This request has been blocked; the content must be served over HTTPS.
Any help will be appreciated.