by design, animation pose output pins can only connect to a single pose input pin. However, you can circumvent this behavior by dragging off the initial pose node output pin into an empty spot on the graph and choose 'Add Reroute Node...' then, you can drag off the reroute node into another pose input pin.
Result: Successful blend of two poses via re-route node
Expected: Unable to use a single pose to blend via re-route node
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-79013 in the post.