Long distance, sight unseen diagnoses aren't worth the paper they are printed on. That said, I'm not using any paper:
Cylinder hang up should not cause the trigger to dwell back on its own. You can demonstrate this on a revolver that is functioning properly: after confirming revolver is unloaded, pull DA halfway, then using left hand grab the cylinder to prevent it from turning further and release the trigger. It should move freely forward (as the hammer comes forward as well).
My guess is that the rebound slide is hanging up, for some reason. This revolver needs to be inspected by someone who knows the S&W DA lockwork.