One of my flow hives had 100% mortality going into fall; most likely varroa mite. I pulled the honey super to store for the winter but left the rest of the brood box intact. Within the last couple of days, our snow has melted and temps have gotten into the 50-60s (F). I’ve noticed quite a bit of activity outside my other two hives, and now I’m seeing bees coming and going outside the “dead” flow hive. Not sure what to make of it. Maybe I should pull the frames and move the hive? I had planned on transferring frames from a langstroth hive into that old flow hive sometime this spring.
Maybe they are robbing out the dead hive. I would clean up the dead hive and store it for next season. Not good having robbers, its a good way to spread disease.
It needs an inspection/autopsy. I agree with Rob @Rmcpb they could well be robbers. However, if the originating colony was in a very warm location, it is just possible that a swarm has found your hive. Inspection is sometimes the only way to know.