Customize blank and Menu area missing

Hello,

Under Appearances, the “Customize” area is blank and the “Menus” area is missing (see screenshots). Also, the site gives a 403 Error every 10 minutes or so while working on it but then straightens itself out. Those are the (3) issues I need help with.

1. Highend theme is up to date.
2. I have disabled all plugins and that didn’t help.
3. However, I switch to 2016 theme and things worked so it seems it may be the Highend theme.

I’m in over my head at this stage and willing to pay HB-Themes Support if you can help me out. Fyi, I have two other identical websites with the exact same theme and plugins and they are both good.

HOME

Thank you!
Jon