Sounds like you could either be
1. Under gassed--- possibly a misaligned gas block and or blockage or a severe leak. (your pic looks like it has the correct length tube, allowing full penetration into the gas key.)
2. Possibly an incorrect Buffer tube, buffer, and or recoil spring ?
Is the rifle picking up and chambering the second round? or just not coming back far enough to grab a round?
Also what trigger is installed?