This might be one of the most trivial bug reports ever…but if you look at Micro.blog - Discover right now, there’s a post that’s been floating to the top for several days now (ie, it’s always the first post on the timeline). Looks like the immediate issue is that particular post timestamp only has a time rather than date + time.
Thanks, I’ve removed it from Discover for now. You’re right, something was amiss with the date/time, messing up the sorting.