Hi Anh,
this is what i find out:
The MB Custom Post Type Plugin causes the error, so that I'm not able to see and open any page, post, or custom post as in the screenshot attached before. If I deactivate the plugin, it works.
I'm still not able to create a new Field Group with the Meta Box Builder.
May I give you the login details in a private message? Or how do you wanna get them?
Kind regards
Gregor