4.0.5 Section content hidden. Click here to show it

I’m having the same issue as previous people. I’m getting the message after each section in the editor “Section content hidden. Click here to show it”. I wasn’t aware of the problem until it suddenly removed a lot of content from the page upon publishing the page.

I have gone through the other tickets and see that I also have the problem with the new backend editor not showing, and the window title text overflowing.

I’m using Chrome.
I have deactivated all plugins.
Cleared the cache multiple times (including hard reset).
Deleted the theme and installed from scratch.
I have tried Firefox with the same result.

What else can I do to finally fix this?

Thanks,
Jesper