problem with the update of page

Hi there
I have bought a theme from themeforest (ECOPARK https://themeforest.net/item/ecopark-wordpress-theme-for-tour-vacation-travel-resort/18730432) that uses your plugin King Composer but there is a problem that always occurs!

If I make a change on a page (for example If I add an image, or I edit text etc), the edit is not saved after I update the page. Everything goes back as it was before the change.
The support of theme told me it was a cache problem but even following their instructions to clear the cache, nothing happens. The problem remains.
It’s more than a month that does not solve this thing. Do you know how this problem occurs?

Best regards