There are many possibilities and it is difficult to pick one without knowing what the bolt carrier group does during the failure to feed another round (doesn't move at all-which would include a failure to eject, moves back far enough to eject but doesn't pick up another round, locks back fully after every round, cycles fully but too fast to pick up another round). Though, outside of misaligned or out of spec parts, most problems are related to a balance of gas pressure and buffer weights/springs. I'm assuming you have an adjustable gas system on the POF upper that could be set too low or, less likely, too high. That can be fixed easily for no cost by experimenting with other gas settings.

Hi Juan and welcome. Just swap the upper, lower and magazine to other uppers, lowers, magazines and follow the issue or lack thereof through a recorded process of elimination and it will pinpoint the problem component pretty quickly. Cheers, stay safe and good luck!