Off set buffer retaining pin will deal with the miss drilled channel in the receiver, since upper locked home is not pushing the buffer back off the retainer pin,
And as for mag not loading when fully loaded, keep in mind that mag fully loaded, means that top round can be pushed down in the mag at least 2/3 the way down. Hence 30 round mag body, with antilt follower, will only have a 29 round capability.
Simply, if mag has problem loading what you think is a full mag, then no problems with on round removed, then the one round removed is the full count capability of the mag.