I am not an Elementor support person, so you can take my comments for what they are worth.
I have seen many similar comments recently, not just about Elementor. I think WordPress has recently started to put a lot of pressure on plugin developers to close certain security loopholes. One of the loopholes is the ability to use certain html tags and tag arguments that might pose a security risk. iframe is one of them. So, what happens is that the editors might remove tags you add that are not explicitly enabled. I don’t know if this is the case with the various Elementor text editing widgets.
What I do know is that there is at least one filter defined in WordPress, wp_kses_allowed_html, that might be used, at least with certain text editors. Here is an example. I don’t know if it is pertinent to Elementor. If not perhaps there is another hook that could be used. In any case, it gives an idea of the issue
function custom_wpkses_post_tags( $tags, $context ) {
if ( 'post' === $context ) {
$tags['iframe'] = array(
'src' => true,
'height' => true,
'width' => true,
'frameborder' => true,
'allowfullscreen' => true,
);
}
return $tags;
}
add_filter( 'wp_kses_allowed_html', 'custom_wpkses_post_tags', 10, 2 );
So, what this code, placed in functions.php, says is that the editor will allow the use of the iframe tag and any of the ‘src’, ‘height’, ‘width’,’frameborder’ or ‘allowfullscreen’ arguments. If you use iframe with any other arguments, the editor will remove the entire tag. This sort of behavior might explain what you are seeing.
Enlightened plugin editors will allow you to configure the plugin to allow additional tags, rather than using across the board logic in functions.php. Of course, they should say that you enable tags and arguments at your own risk.
I apologize if this is not relevant to your problem, but it might give an idea of how to move forward.
