Admin Panel Portion Not Working Properly

Hello – ever since WordPress auto-updated my site, I’ve been experiencing a couple issues. My robogallery plugin worked fine before the update, I have a ticket out to them because now it’s not working since it updated.
I can’t customize my theme (Twenty Seventeen) or even load previews of alternative themes, it just shows ‘loading’. It’s not my computer.
Please help ?? I also had to go to classic admin panel mode with a plug-in. It seemed the new admin panel lost some features that the classic had (example: the ‘read more’ button).

The page I need help with: [log in to see the link]