issue using customize or live preview settings

Hello,
I was customizing my website this morning and at a certain point, when I clicked customize, it no longer brought me to the live preview and the options for customizing based on the theme were no longer available. Sometimes it would go to an error page with the error code “500” stating my page could not handle the request. Sometimes it would just go blank and say “loading” but never load. At first I thought it was the theme so I started researching other themes. When I clicked live preview for new themes by any company, the live preview would not load – it just went to a blank white page for all themes. It seems that the live preview and customize options are not working correctly. I cleared my browser, deleted unnecessary plugins, and made sure all updates were to date but still no fix. Any suggestions?

Thanks!