I recently bought a Canon 6D and a Sigma 24-105 f/4 Art. I noticed that, if the internal GPS is turned on, when the camera goes in sleep mode (after a couple of minutes the top panel turns off except the GPS icon) then the camera wakes up but the lens does not respond and the only way to return to work is to pull the battery off and on again.
I tied with other lenses (a canon 50 f/1.8 II and a canon 24-105 f/4 L) and all worked well.
I tried my sigma lens on another 6D (in a shop) and the bug came back.
I'm pretty convinced it's a problem of the lens.
Could someone repeat my experiment?
1. turn the internal GPS on;
2. take a couple of pictures to make sure everything works:
3. wait until the top lcd turns off (except the GPS icon);
4. try to take a picture.