What if Visual Composer for WordPress isn’t saving the updates you make, even after pressing the save button?
I recommend you to check the status code of the request.
It can be seen in the F12 developer tools of your browser.
In my case it was an ajax post that returned an error 500 from my server, right after the save button click.
To fix it, i went to the folder where the pictures get saved in wordpress /wp-content/uploads/ and then into the folder with the actual year.
There are subfolders with the month numbers and the current month number had the wrong access rights set.
I deleted the folder and created a new one. If the folder isn’t empty you either can download and reupload the files or try to correct the folder rights with ssh.