At first I thought this was due to different instances but looking closer, it's the same post duplicated. I think this is the first time I've seen them together.
I've seen double posts before but they were separated in the timeline, so I put it down to instances.
Same happens to me, incidentally just before I saw this thread. I always thought this might be the case when the next batch of content is loaded, but due to new posts the order has changed. No idea if that's the actual reason, though.