,well yes, seems logical in what you said in your last paragraph. That could be a possibility.
A frictional contact that is open has zero force in all six DOF which causes a rigid body motion error.
Think of a near open contact (i.e. the frictional contact is tracked during the solution, but is open initially). Now, initially, since the contact is not closed, should I be expecting a Rigid Body error or not? What I have seen is that I don't experience any Rigid Body error even when the contact is near open for frictional contact. However, for the frictionless contacts, I usually do.