Updating failed. The response is not a valid JSON response

Now, it is very difficult to have save. I need to save like 3 to 4 times, before it works. Some of my elements are not displaying.

I would suggest disabling all your plugins first to make sure the theme and WP install has no issue.

Can you do that and let me know if the issue still occur with all plugins deactivated?

Sure, I will do so.