You need Click to Move enabled for Interact to work as we would like.

The default action will be to move towards the target (if hostile) and turn auto attack on.
With click to move, it will move the toon towards the target.
Without click to move, it will attempt to hit the target but be too far away.
A friendly target will result in trying to "use" them, for example open their store or menu option such as "look at my goods or set your hearthstone here".

Another thing to check...
If your Jamba has strobe follow on, the interact will quickly resume following.