Sorry to hear about your lockup issue, but very glad that you have made a post about it here.
I just ran a test on my 5D3 and had no problems going through the whole 29 minutes 59 seconds cycle before I got a message that video recording was auto cancelled.
I recorded in ALL-I, 1920x1080p, 24 fps, manual mode 1/50, f/4, ISO5000. Recorded to CF card type Sandisk Extreme 16gb, 60mb/s. I don't have any 32gb card to use for testing.
Camera was stationary the whole time on my desk pointed towards my NAS, so the only movement in the image was a small blinking LED.
I will try another test later with movement in the picture to see if it makes any difference.