Please delete
I think it still can be solved. That most likely happens after importing a base mesh that contains polygroups into Maya or Max. Depending on options they may split each polygroup into a separate piece disconnecting vertices.
If you have your original base mesh and the “broken” mesh in the same place (so that all their vertices are in unchanged positions), you can use a Lattice node with neighbors parameter set to 1 to deform your original mesh the same way as your “broken” mesh is deformed from the neutral to say an open mouth expression. Your original neutral base mesh goes to the first input, the “broken” neutral base mesh comes to the second one and the “broken” expression mesh goes to the third input. You can do that for all the blendshapes in batch.
Hope that helps