I installed the plugin (I’m using WordPress 5.0) and after that I could no longer edit what I typed in Elements (posts and pages are ok). But just disabling the plugin and everything returns to normal.
But, indeed, if I change the “Allow users to switch editors” to “no” everything returns as before. Before “WordPress 5.0” – I would say – since I have no access to the new visual editor anymore!
But for now it´s Ok… I’m used with TinyMCE (that seems to have no function with this new WP version!).