I think I might have the same problem?
The Correx (plastic) sheet that is inserted under the mesh floor usually has a wooden baton attached to it to help it to be pushed / pulled in and out. Mine was a neat fit when inserted, the heavy rain and cold I think has caused either some expansion, or movement, but I couldn't get it out. I lifted the hive up 10mm on one side and inserted under it a piece of wood, then used the hook on my hive tool to work the baton out, when out I sandpapered it down as much as I could and then slathered it in Vaseline, it's still tight to get in and out, but it's workable.... the fact that I have the hive on a pallet in which there is a plank of wood directly underneath the back of the hive, where the baton is, probably doesn't help, as the weight of the hive pushes down on top of it.
Strange thing is, I'm finding a lot of moisture forming on the correx sheet, I'm guessing condensation from the warm hive air hitting the cold bottom correx surface, or it could be moisture coming in from outside via the entrance (which is reduced) and condensing on the correx that way.