i had this too with a poly hive.a swarm was dropped in and the hive left till dark and when i picked it up i realised there was a couple of hundred maybe underneath, when i took the board out they were crawling out of the holes.
they didn't want to go in very well so i just put them all in the boot and let them organise themselves the next morning.
Riiiiiight.
When you gather a swarm direct into any 'hive' box and leave it for the stragglers to join the mass, it is entirely normal that some will follow the scent to the mesh floor rather than the entrance, given the chance!
Which might be why some would put in the inspection board ... I think it would be better to close off the board
slot, so the bees don't get to the mesh, if the thing is sitting on the ground.
I don't think the correx is to blame.
Certainly, if you were trying anything like that, you ought to be checking underneath at the end of the day.
The first time I used the Pane
polynuc for this task, I had quite a few bees on the underside of the mesh floor... which I only discovered when I picked the thing up, having blocked the entrance and relaxed!
Subsequently I've used a strip of sponge foam under the entrance, between box and ground, and ... almost none found the mesh! But its something I try to check early enough in the evening for brushed-off bees to have a second chance to discover the proper entrance!