It's looks like it is from being stung before, or something specific to that area. Could be very high or very low flow in that area?
Usually any of the "major" issues, you would see all the tips are burnt/dieing/algae encroaching, but this is specific, so I would assume it to be a specific thing that touched it there, or too much flow from a direct powerhead. It also wouldn't have been there long, considering if it were too much flow permanently, the coral would have grown around it.
Weird about "birdsnests getting deadspots" it's usually quite consistent. Usually the entire inside is a deadspot in aquariums, because not enough flow gets through the tangle of branches. I haven't had that problem yet, but I do have an acro next to it that wins whenever they touch. I guess I've been lucky that my tank has been stable, and I haven't really had any random events. If something happens it's usually because I haven't been doing maintenance, or had just done something with maintenance, but rarely does something random happen.