The update to Ruby 2.4 requires to install the Remote Access certificate again to avoid security messages from your web-browser.
This process is compulsory for all Run on Ruby machines. With local installations it is only required if connecting from remote devices.
Download the recent certificate from the Certificate link in Ruby. Therefore simply change the visible Ruby URL from
Remote Access URL: https:// . . . . . . :2402/app/manage
Certificate URL: http:// . . . . . . :5000/certificate
For the installation of the certificate please have a look at the following links:
Installing Remote Access certificate on Windows
Installing Remote Access certificate on MAC
or the video instruction below: