When working with targets if you need to use Invoker this could be a problem on different situations this is the reason why State Machines have an auto-generated variable called Invoker.
To make your State Machines as much as re-usable as possible on some case you won't want to use Player as target.
Start Node Invoker
Whitin a Start Node target type invoker can be used.
If Start Node has transitions to other nodes they will also be able to use the Invoker target.
On some triggers like On Tag Enter the invoker would be whatever the object which triggered this.
When using triggers like On Key Down these type of triggers doesn't have an Invoker, so in this case you would need to use the Invoker variable from the State Machine or use any other Variable created with the Blackboard.