From what you are telling me, it sounds like the big flapper seals are not turning/flipping either in or out as needed when the slide is activated.
I have to watch mine when I put the slide either in or out. Sometimes I have to manually help the seals turn in the right direction when I move the slide. In fact the top seal is the worst on mine. I have a 2 ft. step ladder I carry in the truck and I take it in the camper when moving the slide. With that I can see the top of the slide and help the seal get flipped in the correct direction if it needs it. AND it usually does.
I have seen where some have glued a piece of belting on top of the slide, and on the side wall of the slide. The seal will hit that and it will help it get turn in the right direction.
Now, I'm not saying this is your problem without seeing it, but it will give you something to investigate.
Good luck, and let us know what you come up with.