Could be a stall, could be the box temp wasnt high enough to help the brisket push through the stall, although a stall at 145 seems a bit low. Most stalls, on pork anyway, seem to occur at the 170 mark. I've not done enough beef to be sure. I will say 14 hours seems a bit light. I plan my schedule for 8-9 lb pork butts to take 18 hours at a 225 temp setting. If the box is set at 200, pretty unlikely the meat is going to reach 200 without a very long wait. I'd try again, set the 1400 at 250 and see what it does. 12lb is a pretty sizeable brisket.
I believe in catch and release fishing. I don't want to EAT 'em all, I just want to GREET 'em all!