Are the lesions only on the left side, or are there some on the right side as well? I ask because HLLE is almost always relatively symmetrical, left and right. Also, I can't recall seeing HLLE on a foxface before.
Something is also cooking at the trailing edge of its caudal fin - sure looks like bite marks. Fish can be pretty sly - while you are busy watching them for fighting, they are busy watching you and are on their best behavior. one trick that
@vetteguy53081 suggests is to set up a phone and video the fish after you leave the room. Maybe throw a bit of food in the tank to stir things up right before you leave...
Did the spots start gradually, and grow in size over a week or more, or did they just appear over a day or two?
Jay