I found similar results on google while searching on your error message. It is likely related to eliptic curve encryption. But to know this for sure you'll need java.net.ssl debug information to find what exactly happens when setting up your ssl connection.
I'm curious where did you add this parameter in the Mendix Cloud portal? I didn't think we had a setting to customize the JVM options online.
I would recommend contacting support to get all ssl debug information using the parameter: "-Djavax.net.debug=all" this should give you a lot of data about the initialization of the SSL connection. And should provide you a starting point to resolve this issue.
For me the issue ended up to be somewhere completely different.
The webservice I was testing against did not have the client certificate authentication implemented. Probably when sending the request from Mendix with this unexpected document resulted in the above mentioned java error.