WP expert to solve blank page issue

I have an issue that I get blank pages in WordPress when I try to save a post or page. The problem is that not a single error is shown, even with debug on, so it's impossible for me to find the exact error What I tried: - define('WP_DEBUG', true); is on - Enabled php error reporting - All plugins are removed - Default theme is used - WP is up to date - All wordpress files are overwritten with fresh ones. - Same in other browsers - I moved this install to another server - On the same server are multiple WP installs that run fine. - Change default permalinks - Repair database - Compare all files with default install - Tried different PHP versions I copied the problematic site to a test environment. I need someone to work on that environment (I'll provide WP login and FTP details), to find out the root cause, and provide me the EXACT steps how to fix it in the production environment. We will release the milestone once the problem in the production environment is solved