Hi Peter,
It’s due to Wireminds tracking code, please check this

The tracking code is HTML code and it’s embedded to TinyMCE javascript code which breaks it. Did you have implemented some code related to this https://www.facebook.com/WebsiteConsultation/posts/how-to-disable-wiredminds-emetrics-tracking-being-added-to-wordpressthe-wiredmin/1818420068413939/? I’m not really sure how it got there and I can’t recommend any solution.
Try visiting search the word WiredMinds to the file I have provided in the URL and it’s there

It’s not from the theme or any plugins, it’s directly added there. I recommend contacting your hosting provider to see if they have any built-in trackers like that. But based on that facebook URL, it should be your hosting’s tracking feature.
Thanks!