Hmm, that is strange, I have no idea what could be causing that, have you tried your SD card in other cameras, or tried other SD’s in your 70d to make sure the SD isn’t the problem?
Other then that I have no idea sorry.
Wish I could be of more help buy I’ve never seen or heard of this problem before. Of its not the SD card I would take the camera back to where ever you got it and tell them its faulty.