Hi Rick,
That is probably a harmless log record from the webserver (nginx) to incidate somebody tried to access '/healtz'. This could be some random bot or some misconfiguration on your end, broken reference to css or js file for example.
When bots are overwhelming your site, you will get dozens of these logs. Thats why I have a feature Request to turn off printing these logs:
https://community.mendix.com/link/space/monitoring/ideas/3972
Good luck!