I've looked at several previous posts, but it's not clear to me if they relate to the issue I'm experiencing. Just updated to CiviCRM 5.8.1 on Joomla 3.9.1. Currently the HTML editor is missing on mailings and events, it's just a box with the straight HTML. The error console is giving the error
id.split is not a function from the angular.js file.
Also missing is the Configure CKEditor button. When I check the demo, I see it there, but it never shows up on our site when CKEditor is selected. I also tried installing and selecting the TinyMCE plugin as the editor, but again that makes no difference in the edit window. I'm getting this error in the Display Preferences page:
Empty string passed to getElementById().
I've cleaned the caches and checked that the Resource URLs are correct. Unsure what to troubleshoot next.