Hi gameba - Happy New Year to you too!
I took a look at your capx - weird problem caused by the layout restart. I suspect that it was a combination of the Box2D+ library not coping with the destruction and recreation of a large number of recycled objects all at once. You see, when you set an object to Box2D+ Enabled then the body is destroyed and then recreated, including all joint references. The bug was caused after the layout had restarted.
Here's a capx that contains the fix. The link object default is set Box2D+ Disabled, then - in the joint creation loop - there is a check that the links are disabled before they are set enabled. Before, the links were set enabled twice, once by reference through the family and then in the next loop iteration by reference directly by the link object condition.