I am familiar with the material you are talking about covering the tops of the slides. It feels like a rubbery kind of membrane. To me it feels like the white waterproof first aid tapes, ankle and wrist wraps we used in high school sports. My first guess would be that there were air bubbles under it not allowing it to lay flat, which it needs to be. As to how the air bubbles happened is anybody's guess. But most likely it wasn't laid down flat and then had the air rolled out from under it. Another issue I have seen cause air bubbles are when the material isn't folded correctly and tight over/around the corners, that will let air back in under the material. Depending on where the air bubbles were located they most likely got pinched and then cut when retracting the slide. I had that issue on our 2014 5th wheel. A friend of ours had it on their travel trailer also. I used a wooden rolling pin on mine to get the air out. I used a spray on sealer to glue my fabric back down along the edges of the cuts. Sprayed over the top of them with several coats. Then when that was dry I spread a thin layer of a good silicone sealer over that. Lastly I put some tarp repair tape over the top of the sealer when it was dry. The silicone stays sticky and I didn't want to risk those spots catching on the slide seals when moving the slide in and out. The tape keeps it smooth and non sticky. I haven't had any problems since and no signs of leaks. I also had to "re-do" one of the corners on my big slide. The material was so bunched up there, it was like a knot and had some openings that I am sure water could get in through eventually. I sealed that up with the good quality silicone too. I got both at Camping World. Can't remember the name or type of the spray on roof sealer. I felt that this was a manufacturing issue, or quality control issue, but just fixed it myself so it was done with. I haven't had any problems with it since. We did the same things to our friends travel trailer and it fixed things for him also. I think these are just one of the things that have to be checked periodically and have routine upkeep done on them. Like you, I meticulously take care of my things and this still happened to me also. Just glad I caught it before it caused any real serious problems. Now that I know, its on the list of things to keep a routing eye on.