[MAYBE SOLVED] HTTPS site losing PHP connection overnight!

I have an Ubuntu VPS server with over a dozen sites and recently added a new free domain with CI4. The site still opens a index.html but PHP is not working?

For the past couple of days I have had to reinstall the Certbot certificate and that cured the problem. 

Now the PHP is giving the following error report:


This site can’t be reached
MyNewSite.com unexpectedly closed the connection.
Try:

• Checking the connection
  

[color=var(--error-code-color)]ERR_CONNECTION_CLOSED[/color]


Any suggestions as to where I should start looking for the problem?