I’m not really sure what would be causing that. As I said, everything looks okay in your screen shots.
Is it only the Things tab that doesn’t display anything in the builder?
What about the Categories tab?
What happens if you create a new tab and add components to it - does it work?
Okay, that’s really odd. I just checked your published App again and all those extra components are visible.
Did you say that it works okay in an incognito tab?
I wonder if you may have some browser extensions that are blocking it or getting in the way?
If you do have any extensions installed, try disabling them all and then see if it works.
If it does, then you can try enabling them one at a time until you find which one is the problem.