This is from the front wheel of my trainer bicycle. In November, I patched a flat (patch is still good), and remounted the wheel on the trainer, pumped up to 120 psi. Neither trainer nor wheel has moved. Last week, flat tire. Today I removed the front tire and found this 2 inch cut. 700x25 tube. Pretty new. Tire is near new. This is an easy tire to mount, and I use no tools in remounting it, only my hands. Checked carefully for proper tube seating, as I always do.
So, what is going on here? Rim tape is great. This cut is on the bottom of the tube. Trainer has not been moved in any way. I have sat on the trainer for several hours while training.