Mysterious. It worked for me when I added
You could verify that you are looking at the correct solution.properties file,
it must be in the solution directory,
and the property should not be redefined with another value later in the file.
Your SDI version has the required fixpack level.
If everything else fails, create a small AssemblyLine (cert) with just the script to import the certificate, export this to p.xml, and add this property to solution.properties:
Then run the Assemblyline from the command line:
./ibmdisrv -c p.xml -r cert -R
and look at the debug output. It might give you a clue as to why the SSL handshake does not transfer any certificate.
Remove the javax.net.debug property from solution.properties afterwards, it produces too much for normal use.