Ot, thank you for the information. You have have half a brisket, either the Flat or most likely the Point cut, doesn't matter a lot in a very long cook.
Cooking started at 1000 Friday and continued until at least 0400 the following day, for 18 hours. We know that at 135F Pasteurization is achieved after about 5 hours in a 3-inch thick piece of meat. (Baldwin 2008, Table 5.1)
FYI, Pasteurization is the substantial reduction of the potentially harmful pathogens of Listeria, Salmonella, and E. Coli to the degree where they can no longer be considered harmful. Your meat was more than safe for consumption at that time.
Next we have to consider what happened sometime after 0400 to cause Anova to "beep", and presumably stop operating during the next 5 hours. Was it the result of low water level? Most likely as that Colman cooler has 1 1/2 square feet of surface area which is a lot. We know that significant water loss occurred from 1000 to bedtime. Thus in future long duration cooks more water is likely needed to be added after similar durations of time if you don't take steps to reduce evaporation such as floating plastic film, a cover, or ping pong balls.
Since the brisket was Pasteurized, and an intact cut of meat, and for personal use within the home only for people without a compromised immune system. I would have continued to cook the meat to completion as its core temperature would have remained higher than the water temperature.