Can't edit a page.

I can’t edit one single page in an otherwise perfectly running site. The site is: https://www.brasch-group.com/ and the problematic page is: https://www.brasch-group.com/brasch-group-news/

Could the reason be that the page is too long? It displays just fine, but when I try to edit it, I get a blank screen.

I have tried to upgrade to the latest version of WP to see if that would help. Unfortunately I can’t, because my host 1&1 is behind in upgrading to the required version of PHP.