y’know gbx, this happens about 1/3 of the time solo. they fly though a mountain side, which your bullets collide with but they don’t and then they get stuck or they otherwise get stuck outside the map.
If one is lucky, a chain lightning, norfleet or mm can put them down, sometimes.
They are usually BA Surveyors so Chain lightning tickles them. I’ve never been able to kill them with anyone other than Sal dual wielding Topneaas. They regen faster than anyone else can shoot rockets.