Unfortunately we have got word from Apple that this is a known problem effecting many of the plugin developers, There is a problem in their render path when stacking effects. We are waiting for new information from the FCP X team.
Not everyone with FCP X 10.0.6 sees this problem, it depends on your graphics card / memory / OS version / other hardware combination. At the moment the only 100 percent fix we have for users that see this problem is for them to go back to FCP X 10.0.5
For some users updating drivers or other software versions has fixed the problem.