Hi there Mitchell,
Thanks for writing in, have you also ran through these steps?
1: If you have any caching plugins make sure they are deactivated for testing purposes and ensure all caches are cleared.
2: If you are using Cloudflare make sure it is in development mode. If you aren't sure what cloudflare is, you can ignore this step.
3: Remove any custom CSS/JS added. A small syntax error will prevent the preview from loading.
If you have and it still isn't working please post some WP Admin Login details in a secure note and we'd be happy to further debug this for you.