Pop-up error that just won’t go away

Hello,

The problem I’m having was occurring long before several upgrades of wordpress to the current version. I formerly had a TinyMCE plugin, and it wasn’t the same one on all of my sites either. I started getting this annoying error popping up any time I wanted to edit or start a new post:

Deprecated TinyMCE API call: <target>.onNodeChange.add(..)

I tried to find out what was causing it, and several answers I found in the forums indicated that it was related to the plugin, so I got rid of it. Even after that, and after transferring hosting, I’m still having this issue. The tech from my current host said it was because there was an outdated plugin on my site.

So after I had created my multisite, and moved it to this new host; I went through all of the sites, noted the plugins, verified the compatibility with my current version of wordpress, and eliminated/replaced all the outdated ones with new plugins that basically do much of the same things.

But regardless of all of this, I am still having issues with this pop-up error message. Today too, I attempted to activate Jetpack on one of my sites, and it activated, but then when I clicked activate the recommended features, I got something that indicated a syntax error. I don’t know what that is, but I have a feeling that it is related to this other error issue.

Anyone responding, please consider that I am barely computer literate, so please explain your answer or give your advice in plain English, indicating exactly where to go/find whatever it is you are explaining. Thanks so much!