Hi again,
since I have the full control about the Chat plugin from the Facebook webpage – I can change the style of the chat window – why I simply can’t disable it from there?
We wouldn’t know why you can’t disable it from there as this is the native Facebook chat solution, and only the Facebook team would be able to confirm.
I believe it is because it wouldn’t make sense to disable these from Facebook directly—if the user added it from their integration, it is because they would likely want it there. Your case is a bit different because you are having issues disabling it from the integration.
I see you’re using a staging site. Could you try to disable the following plugins for testing?
* PixelYourSite: by PixelYourSite – 9.2.1
* WPCode Lite: by WPCode – 2.0.4.4
Also, I mentioned flushing the cache on your site (page, browser, and object cache). Could you please confirm that you tried that? Often some hosting providers add caching to your site, so you can check with them as well to confirm.