Thank you very much for the prompt reply.
It stuck at
The update process is starting. This process may take awhile on some hosts, so please be patient.
Enabling Maintenance mode…
Updating Plugin Jetpack (1/1)
for hours. So, I close the browser and I can’t access admin panel because maintenance mode enabled.
That happens twice and I write this review.
Short story,
I modify my wp-config.php as you sugested. Then, I downgrade my Jetpack to 3.9.6 so I can update to 4.0.2 and show you the debug log. But nothing happened! It upgraded successfully and working fine now. I have no idea what’s wrong before ??
