My Vultr VPS is running Ubuntu under CloudPanel and hosts about twenty WordPress sites. After applying routine server updates today, most of those sites now show either a completely blank screen or a generic 500 error; only five are still behaving normally. I have full access to both CloudPanel and SSH, so you can dive straight into the logs, check PHP-FPM, Nginx, MySQL and any package dependencies that may have broken during the update. No individual site settings or plugins were changed—only the underlying server stack—so the issue is almost certainly at the system level. What I need is a swift diagnosis and a clean fix that restores every affected site without disturbing the ones that are still online. Once everything is stable, please leave me a short summary of what went wrong and the exact steps you took so I can avoid the same outage in future. Acceptance criteria • Every WordPress site loads normally—no blank pages, no 500 errors • The few currently healthy sites remain untouched • A brief post-mortem outlining the root cause and your remedy