In your current setup, the simplest way to get this to work is to save the pawn that was detected in OnSeePawn to a variable (assuming it passes the cast check), and then use that cached variable as the input to TargetActor for your MoveTo section.
You can save it to a custom Blackboard entry or you could use the AI’s current AIController to cache it somewhere else (a member variable on the AIController, or the possessed Pawn, etc.). If you use a custom Blackboard entry just make sure the Instance Synced flag is NOT checked so that each individual Blackboard can track its own target.
