I can’t hover over the circle and take a screenshot, but if you were to hover over that circle, it would say “unknown/deleted user”.
I know who liked it. The user is still very much there. In fact, I still have their notification at the top of the list:
I went back through the entire thread, and I can’t see anybody’s like except the posts where I liked them, for example this one.
My guess is that the data is still there, but maybe there is some kind of permissions issue keeping it from being queried. ¯\_(ツ)_/¯
I have no idea if admins or moderators can see the likes. If they can, then I would suggest looking at the thread in incognito mode without being logged in.
On Discourse, the user shows as blank if you have set the user as either “Ignored” or “Muted” in their profile menu. That is potentially why that user is blank.
I have to check Meta, the Discourse Support Forum, to see if any other reports are known but that is my guess at the moment.
It’s happening even on topics with brand-new users whom I haven’t interacted with. They haven’t had time to hate me and mute me yet.
And I can see it when I am logged out, too.
Oddly enough, it is not happening at a 100% rate. On this post, one like is exposed and the other one is blanked out.
Hopefully it gets resolved soon!