Hi Victor, hehe you found the 2.0 designer before we were able to announce it yet .. that to come soon :)
There should be errors in your server logs that indicate a possible reason (also check JS errors), but the most likely reason is that you would need to also upgrade your Guvnor version to 5.3.1 to get it working because I would venture to guess that there was an issue with saving your process bpmn2 into Guvnor. You could test that by using the Guvnor rest api and check the source of your process with like
localhost:8080/drools-guvnor/rest/packages/<yourpackage>/assets/<yourassetname>/source.
Hope this helps.