Automatic video stop on SDCX class 10 card
You could try a new card. Could be the issue. My guess it's the camera and the heatsink on the sensor. 

Try a different card first to see if that solves it. Card's can go bad. But with the Canon line (and all DSLR cameras really) do have issues with overheating- especially as they age. 

If a new card doesnt fix it, you can try to service the camera, perhaps it just needs a good blow out/dusting of the heatsink. 

Canon, Sony, Nikon, most models have had some sort of issue at higher resolution video/frame rates with heat issues, and as the cameras age the cameras don't behave as well as when they were new.