Java Web Application HTTPS works only when -Djavax.net.debug=all is set

I have a Java jetty-based web application that I am migrating from HTTP to HTTPS.

I was experiencing difficulty connecting to the application over HTTPS - the request would just hang and eventually timeout.

I then set the JVM option -Djavax.net.debug=all to try and debug what was going on and to my surprise I was able to connect over HTTPS.

To make sure I was not going mad I then removed the option and once again could not connect over HTTPS.

This is very puzzling to me - I thought this option would just affect logging behavior, not actual application behavior. Does anyone have any idea what could be going on here?