I am gatering thoughts from people who use the "Lock" option for meshes. I understand that once a polygon is meshed one may want to lock it so that it is unchanged - fair enough. However I found that as the meshing task progress NX may "fall" over when significant mesh update may be required because some meshes are locked.
Consider the case where one has meshed some bits of geometry and one is happy with it. One wants NX to mesh any other polygone attached to the "locked" mesh by taking account what is "frozen". It cannot be changed!
Benefit of locking is when you want to do mesh morphing. Mesh morphing is to maintain all element and grid ID while do slight dimensional changes at the global scale of the mesh.
If you think that locking is affecting the mesh update work, probably you can choose to change the locked mesh into disassociated mesh. This will free the polygon face/body, and also maintaining the mesh you want.