I think a lot of times if one moves after being stationary for awhile...assuming nothing else has changed (like you moved a powerhead), it is because it is looking for more food...trying to find a position that it can catch more food. So keeping them fed well help keep them in one spot.

I would manually remove the one you have pictured and find it another potential spot. IME it will eventually find its way into that powerhead. They tend to move toward the direction of flow...which right there is the intake of the powerhead.