I have another instance on the same host with most of the same plugins. It shows the same error, but I can see all the expected TinyMCE buttons. So it doesn’t appear to be this error alone that is causing the issue.

The plugin you are referring to (compat3x) is from the wp-includes folder, so it comes with the WordPress 4.8.

• This reply was modified 7 years, 3 months ago by trisym.