We have issue with EE and the wysiwig editor.
We are running last version of WP with Theme Avada, everything is running fine regarding the tinyMCE plugin when editing pages, posts, …but when we try to edit an event in EE, the controls on the tinyMCE do not respond, dropdown are not working and/or the drodown menu selection are shown above the wysiwig editor.
see screenshot here https://imgur.com/wo3Z5E1
If you temporarily switch to a different WordPress theme, does the issue persist? You can use the theme test drive plugin plugin to troubleshoot this with the twentyseventeen (or similar default theme).