I have had difficulty getting swarms to stay in a couple of Flow hives. If they are a 10 frame boxes and the swarm isn't a very big one, and particularly when there is no foundation on the frames the bees tend to abscond. So the trick I have been told, is to cut a section from a plastic queen excluder and tape that to the front of the hive so that even if the bees want to abscond the queen cannot get out! I am trying this on a box at the moment so I'll let you all know. The only problem I can see is if it's a secondary swarm and the queen in unmated she can't get out to go on a mating flight. I will give it a day or 2 and see what's going on in the box. If there is comb being produced, or dare I hope for cells with eggs, I will remove the queen excluder.