@Keni, re. the OP.
I agree with some of the posts here that there are bound to be some oddities when importing projects from Pre PC versions of Sonar.
I would have thought it would have loaded the default track and bus plugs, but perhaps the way tracks and busses were coded is different now, and this throws a curved ball to X3.
Also, like mettelus, if I advance a project through versions of Sonar, I immediately save it with the version number/name in the title, so I know "what was edited where". Some have moved through three or four versions, with no major issues so far.