Stovepipe can be either too much power/cycling too fast, OR too little power and not cycling fully. Or just a problem with the ejector... spring weak, damaged, or fouling causing it to stick.
In your case, if you didn't make any changes to the upper and you're using reasonably hot loads, very good chance that the cycle speed of the action is too fast and the case isn't getting out of the action fast enough before the bolt closes on it. You need to retard the cycle speed, which could include reducing the amount of gas, using a longer gas system length to change the timing, a heavier buffer to slow opening of the action, or a buffer that absorbs energy at the end of the action cycle as it hits the back of the buffer tube.
Quoted:
Could be a fluke, but for one to base a fatal flaw on only 4 rounds after a component change isn't right. You gotta really test drive that thing a little more.
Agree that 4 rounds isn't a very extensive test.