Tearing of the vinyl floor under the slide is quite common. It happened to us. In our case it was caused by a loose AAA battery that was overlooked during pack-up. It can also caused by a mere pebble on the floor. There is not a lot of clearance between the slide and the floor. Our tear was about 1" x 6". Had a hard time matching the floor pattern locally and reached out to Forest River. They told me what pattern it was, but they no longer used it. They referred me to the actual manufacturer "BEAUFLOR". Unfortunately, that pattern had been discontinued. I wound up cutting a matching section out of the pass-thru to insert where I cut the torn piece out with a utility knife. I used Perfomix VLP to cement it in. The Performix VLP literally fuses the vinyl together. I then got a small "sample" piece of vinyl (close, but not a match), from Home Depot and repaired the cut-out spot in the pass-thru.
In your case, a 6" x 12" tear raises a red flag to me. Either something pretty large is stuck underneath or the slide floor has come loose. I'd run the slide out and get underneath it to inspect for loose flooring or fasteners. Also, worn rollers can also cause floor damage.