It was a relative new 70d, in good condition. Working well with Canon EF lenses, with Tamron lenses – but NOT with two different Canon EF-S.
The lenses work well with other camera.
Cleaned the contacts. Nothing.
Trying to rotate the lens in the mount, in the limit of the blocking pin. Nothing.
(The camera was by my customer, I talked to him only through emails, giving ideas what to check.)
After approx. 2 hours he found out, that 1 pin from the 3 power pins of the camera was a little bit shorter, then the others, and probably the lens mount of that two EF-S lenses were not exactly the same, like the others.
Nice. I hate any paranormal phenomena.