Hey Scott, welcome to the forum.
I had this exact same issue on the first time I flew it. I was running my 4s pack, and when I would do a punch out, it would just die, completely. I took it up pretty high and let it fall and tried to catch it at the last second, but it just slammed into the ground after a very brief motor spin up (less than a tenth of a second).
Since that day though, after flying it on 3s for a few packs, on my 4s packs now, it won't do it. In the LOS video I did I tried to get it to do it so that I could have some logged info of what is going on, and there was nothing. At no time did it just quit. It flew perfectly.
If you can, take your quad out with an SD card in it and log the flight. Try to make it die like it has been doing while logging and then upload that file here to this thread. You may need to put it in a .zip folder for it to upload. But once you do that, I will take a look at the file and see if I can see anything that is pointing to the issue.
