Sforno on Deuteronomy 18:8/ספורנו על דברים י״ח:ח׳

1לבד ממכריו אל האבות, the members of any priestly roster, known as בית אבות or as here. plain אבות, do not have the right to share their sacrificial meat with their relatives or friends except when this meat was part of the daily or weekly public offerings. These may be shared or exchanged between different rosters. However, any offerings brought to the altar on the pilgrimage festivals are not subject to the authority of the priestly roster officiating during that week at all. The expression ממכריו, “of his acquaintances,” does not apply to the days of the festivals. Therefore, the Torah orders that on that occasion basically any priest present may eat a share of such offerings regardless of whether he belongs to the roster of that particular week. This is why the Torah writes; חלק כחלק יאכלו, of the offerings presented during the festivals all the priests enjoy an equal share.