Well, lo and behold, done a lot of trouble shooting this morning. And to cut a looong story short, it turns out that the old girl, Logic, still suffers from old coding(thus the name "logic" often seems to be misplaced ). At least with the 10.4.8 version in this case. Logic have a controler path problem, if tracks resides within Track Stacks(witch was the case here). It doesn't matter what plugins you use, assigning an external controller to the Smart Control parameter, doesn't work. The Smart Control parameter have no problem communicating with the plugin, but you cannot assign an external controller to it. Tried dishing sc and plist several times inbetween new sessions...new ones and old ones. The new account as well.
So, as long as you stick to Audio tracks that aren't part of a Track stack, you're good. Having assigned an external controller, and then moving the track to a Track Stack, also interrupts the connection. You can, however, use a VCA.