White screen of death on post save only

Question

I've worked in WordPress many years and never seen this particular behaviour. The white screen of death only shows on Post Publish or Update. It doesn't show on WooCommerce Category additions. It doesn't show on plugin additions, etc. The front side of the site shows just fine.

No PHP error shows with WP_DEBUG is set to true. It doesn't change when all the plugins are deactivated. The wp-config and .htaccess files seem to have the correct address settings.

When the back button and refresh are used, the changes show, so I think this is a redirect problem. It's just not redirecting to a confirmation page. What could be causing this problem?

New information: three of us were working on the site in a work meeting today, each of us has our own logins. Towards the end of the session, one person, who had entered 51 posts successfully, had the white screen of death on all dashboard addresses. But, two of us were successfully logged in and working. Now two of us have the white screen of death. The irregularity in the problem is puzzling.

Answer 1

Per the comment on the original question and work with hosting technical support, the problem was indeed the child theme. Both the comment and tech support gave me a possibility to pursue, but not a conclusive answer. So, here is how I pursued it.

1. The parent theme was Twenty Sixteen. The child theme only had the very basic code required in functions.php and about 50 lines of CSS changes.

2. To test whether the problem was indeed the theme, I installed Twenty Seventeen and activated it. It activated fine, and I was able to edit a post without the white screen of death.

3. Then I went through the same procedure to create and activate a child theme using Twenty Seventeen as the I had for Twenty Sixteen. I was able to edit a post without the white screen of death.

4. I deleted both Twenty Sixteen and the Twenty Sixteen child theme.

5. I re-installed Twenty Sixteen and copied the child theme from Twenty Seventeen, changing the folder name and the template. At this point, the child theme was using all the resources of the parent theme. I was able to post and edit without the white screen of death.

This brings up the further question of precisely what caused the child theme to break the posting functionality, but at least we can move forward with the site construction.