Jean-Philippe ARDENOY

After some further research, I found out too main fixes for this:

1. for whatever reason, the header X-Frame-Options is not correct and should be corrected with this code in .htaccess

Header always set X-Frame-Options SAMEORIGIN

and/or this code in your function.php

add_action( 'admin_init', function (){
	header_remove("X-Frame-Options");
  	header("X-Frame-Options: SAMEORIGIN");
},PHP_INT_MAX );

2. you have an Adblock plugin in your browser seeing the editor’s iframe as an ad. So you have to whitelist the website.

In my case, it was the Adblocker.

Now, everything is back to normal. Hope it can help some of you ??

Same here. Not sure if it comes from Chrome but the plugin sure needs an update about this or, at least, a workaround. Did anyone code something yet?