The cause can be that your web server is configured with PHP settings that are too low for a theme with several plugins - specifically max_execution_time and memory_limit. Thus, the web server is rejecting to save the theme options. This is not a theme fault or bug.
You can get your web hosting company to increase your PHP limits, as required here https://elementor.support.vamtam.com/support/solutions/articles/262353-recommended-php-limits-and-php-version-vamtam-elementor-themes