Hi Brian,
Setting your temp to 250 for brisket is probably the culprit here. 225 is my "go to" temp for any large cuts (briskets and butts). You mentioned you had the "alarm set on the probe;" is this a PID, or external thermometer (like a Maverick)?
But, how was the brisket? Was it tough, or overly dry? Some cuts do cook quickly. I once did a 9 lb pork butt overnight that I expected to be done about noon. When I checked it at 7 am, it was within 1-degree of done! Sometimes, the meat has its own schedule.
For brisket, especially, I'd lower that temp. Low and slow is the ticket!