Hello,
Our theme is not the reason of the issue because it happens even with the default theme! If their support had try to enable the default theme they saw this, so I don’t understand why they blame our theme, it’s ridiculous. Hight level support of the Elementpor plugin ? .
Anyway, I found that issue appears if Load Files asynchronously option is enabled in Rev slider options https://prnt.sc/1erh3ce Probaly Elementor does not support Async loading of Files. So, keep this option disabled and tell about that to Elementor support because the Revolution slider is one of the most popular sliders for the WP and it’s good to be compatible with that.
Regards