According to Roger Cicala and Aaron Closz of Lens rentals, Some serious sensor defect present in few models of Canon T6s and T6i, if you look at the sensor image (below) captured from a 10X microscope lens the you will see many tiny dots present in the surface of the sensor… it’s look like some dust of or other particles stuck in between the top layer of sensor glass and sensor.
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.
The affected cameras all had a dramatic pattern that at first we thought was oil or dust on top of the sensor glass.
For more details see the article at Lensrentals.com
I can confirm, that Canon have a production problem.
Particles stuck in between the top layer of sensor glass and the sensor.
Return the camera and demand a error free version.