From the LensRentals Blog:
"Every once in a while we notice something, because of the large quantities of cameras and lenses we buy, that we think people should be aware of. This particular issue won't affect our renters; we've sent the affected cameras back. It may not affect very many people at all, since this is from a relatively small sample size. But I still think it worth mentioning.See the entire article on the LensRentals Blog.
The bottom line is that 4 of the Canon T6s and 2 of the T6i cameras we received had to be sent back because of a defect in the sensor stack (the layers of filter glass over the sensor). This is out about 10 copies of each; the others were absolutely perfect."
We checked our own Canon Rebel T6s review camera and there was no indication of the defect. We have no idea how widespread the issue is, so be sure to check your own Rebel T6s / T6i cameras upon receipt.