So I think I have solved this. I’ll leave it up to the sages and the team as to whether this is a feature or bug.
The leader endpoint loses its place when I click on the bounding box of the text for any reason, whether to drag and move it or to double click on it to edit it. I can click and drag the stem or the branch of the leader line itself to my heart’s content and it stays. I can edit the text box as long as I double click in the text box and not on it.