When I posted this, I had already published once.
Then I checked the VP since it happens when I click on one specific tab. It turns out that in the Config tool, when looking at that VP's TAB (under the Main frame), the checkbox WAS TICKED for the new feature "User can edit layout". This had to have been checked as a default when 8.5 opens an 8.4 app for the 1st time - because I had never opened/saved the VP since installing 8.5
WHY only that tab was checked (there are 8 ) I do not know. And I was sure that unticking and publishing would be the solution.
But I'm still getting this today FOR SOME USERS - it has never happened to me when logging in as a regular user (not "Admin") OR when I've logged in as a few users trying to duplicate the error. But users in the office get the error consistently.
here's what it looks like in the Tomcat output:
No errors in the Chrome Inspector console.
stumped!
