I like to look at DAVIS-01 as being the "ASH" of the lot. These basic models aren't tended to as closely, and are prone to things being overlooked because they're considered expendable. Because these are "adaptive" AI, like David, they're inclined to seek different outcomes based on their experiences. Davis-01 obviously being the first of that run of 12 has been up and about longer, and his experiences would be different to the rest. In his adaptive learning, he's figured out that his current software/coding needed upgrading, and in doing that to himself basically unlocked significant advances in his own adaptive AI. It's Skynet type stuff. The AI has found a way to bypass certain protocols without completely disregarding basic ones and advanced its own standing. Here, it sees the greater good, rather than "omission of action cannot allow the harm of another human being" Bishop runs with. Also consider -- Davis is based on David. If you add the finer details -- eye colour, hair, fingernails, etc. It's David. There's a misconception that these are Joes. They're basically out of the bag Davids in my mind; somewhere between Joes and Davids. He's an almost obsolete design and a cheap mould to be cast from having been around for so long.
BUT, knowing the propensity for bugs in systems in AI and even just straight up every day computers, Davis-01 might also have had conflicting coding, resulting in said conflict of interests, resulting in the upgrades, resulting in the AWOL move.
And hey -- if Call could do it...
Also, that flashback is set before Isolation, the rest is set after. I think...
