It may be helpful to print more details about handshake messages if -Djavax.net.debug=ssl,record,packet option is specified.
Comments
There are a lot JSSE debug log enhancement in JDK 11. Close it for now.
07-02-2019
See also Xuelei's comments in http://mail.openjdk.java.net/pipermail/security-dev/2016-August/014506.html
02-08-2016
For example, please see enhancements in the following webrev:
http://cr.openjdk.java.net/~asmotrak/8159416/webrev.03/
It updates DTLSInputRecord and DTLSOutputRecord classes to print sequence/epoch numbers and names of handshake messages.