Boom bots must always keep moving. I don't know why they sometimes stop in the middle of an attack command but they do. It would be awesome if this bug could be fixed so that boombot behaviour is more reliable. Also, im not sure why they blow up against walls.
Walls are an enemy "unit" for all intents and purposes. TA avoided this problem due to the fact that its walls were wrecks, not units.
Which honestly should be the same in PA. Walls in TA had a downside to them as that your own forces could not simply fire through them, making them more a strategic choice instead of a no-brainer.
I actually enjoy the bunkering gameplay that is possible with the walls we have now. Good defensive movements can make a huge difference, and likewise maneuvering around a fortification can seal an assault. I think it would be a better solution to just do an edge fix so boom bots only target walls if focused down on them.