localhost refused to connect after upgrading to High Sierra After upgrading Mac to High Sierra and some other upgrades there is a problem connecting to localhost.
Actually, upgrading to High Sierra was OK but according to the Mac update history the last update was to MacOS High Sierra 10.13.3 Supplemental Update.  It was kind of strange because the problem started after I hit restart with update but this update required one more specific restart.

The Spring Boot applications work fine. I can connect to them from a test client using opened ports. A connection to the Apache server form the browser also works fine. However, the browser connections to my applications are not working
The problem was that the Chrome security certificate required for these applications stopped working after upgrades.  Reinstalling the certificate solved the problem