I am not sure whether it is a bug or not, but sometimes some leader arrowheads of tags look weird in a specific view in Revit. In other views, same leader arrowheads and tags look ok, so I believe it is not a matter of the leader arrowhead itself.
To fix this issue, you have to manually drag a blue dot control point at the midpoint of the leader like the image below. Once you drag it to somewhere, then the graphic issue of leader arrowhead will be fixed.
If you want to have exactly same graphical expression of the leader, you can simply drag it back to the original position.
I started to publish a article serially in a monthly Korean AEC magazine titled “CAD & Graphics”, and the overall topic is “How to create a beautiful drawings using Revit graphic functions”. First article for this month is about general introduction of each graphic functions in Revit.