That was an interesting question. Was it deleted? If so, why? The browser record links to Page not found. If it was moved to another SE, there should be a redirection or something.
Here's the link to the question, which was deleted by the author (you need 2,000 reputation points to view deleted posts). A user suggested in the comments that this question would be helpful, and the author responded that it did address their question, and chose to delete their post because they felt it didn't need to be kept around. There weren't any serious issues in general, and nobody had written an answer - really just a couple of comments discussing the duplicate.
I'm OP, so I'll shed some light on this.
The reason I deleted the question was a combination of:
- I'm a bit of a privacy freak and the question itself contains my exact location at an exact timestamp.
- The way @B--rian responded in the comments left me with the impression that it's completely obvious to anyone in this space that it was a lens artefact. As in there are thousands of photos just like this one (or close).
So from my PoV it didn't make sense to make a minor privacy compromise in order to leave a "doh" question documented, unlikely to serve anyone.
I specifically asked @B--rian to post his comment as an answer so I could reward him for the effort, but he explicitly elected not to. So that wasn't part of the consideration either.
As pointed out by @uhoh, I'm now completely convinced that it was a lens flare as the effect exactly matches the one found in the first photo here.
Given that there is some interest in the question, I'm reopening it.