Tied interfaces are a complex feature and it is easy to have a conflict between constrained and primary definitions. This check highlights inconsistent definitions, for example where a node might be included in both constrained and primary surfaces.
Tied interfaces allow two sets of elements that do not have connectivity to be joined without the need for complex mesh refinement. Instead the elements on one side are taken as primary and the other side as constrained. The nodes on the boundary of the constrained side are tied to the nodes on the boundary of the primary side through a set of constraint equations.