I was having a very similar issues. Cleaned all the threads made sure everything was clean. New AW 18490s and it was still happening. Also tried a brass battery tube with the same results. What I finally did that seems to have fixed it was remove the positive screw that holds the tube mount to the body of the device and cleaning the top of that and where it mounts to the body. It looked pretty cleaning but there may have been some residual oil or something left over from the machine process that was preventing it from getting a good ground connection. batteries used to come out at 3.8-3.9, the batteries after the cleaning are reading at about 3.4-3.5. So it was a pretty dramatic improvement.
