The expansion joints will throw off the center of mass of the entire shell, leading to a positive feedback loop of orbit decay and expansion compensation. Without coordination, this is catastrophic. However, coordinating nodes are light minutes apart, making timely coordination impossible.
Why do you think it's impossible? To me, it seems like all effects (eg. mechanical waves) would propagate at much slower speeds than the speed of light. This kind of control system experiencing significant delays and dead-times is not uncommon.
You need a force to balance the change in orbital velocity due to expansion or contraction of an expansion joint of a fully connected shell; otherwise, the shell will begin to wobble. The forces would be enormous and tear the shell apart from multiple places.
One solution is for the expansion joints to have infinite range— a disconnected swarm of platforms which is exactly what a Dyson swarm is.
