I have the same problem too.
I am using WordPress 4.8.2 with theme Fluida and Yoast SEO 5.7.1. And once I try to create a new post/page, the website show up with error500 time-out.
And I have tried deactivating Yoast SEO and the problem is gone. So I think this is a problem with Yoast SEO. What should I do in order to solve the issue? Thanks!