They seem to be confused over scriptural aspects of the Passover and man-made rituals that developed from them. In the original Passover, Israelites were gathered in their homes and required to slay a lamb. In Exodus 12 we learn that Israel was to roast the lamb and eat its charred carcass with unleavened bread and bitter herbs.
This is hardly a feast. It was a solemn memorial, eaten in fear (12:11—where “haste” is the Hebrew chaphaz). Widespread death of firstborn was about to occur; therefore it was a solemn, apprehensive time, just the opposite of a joyful feast or fellowship meal.
Perhaps this group’s practice is a take-off of the Jews’ traditional meal called Seder, meaning “the order of the ritual,” on the 14th prior to their Passover on the 15th. The Seder grew out of the biblical Passover on the 14th, the true Passover time (Ex. 12:6). While the main Passover was kept at the Temple, the Seder was kept as a family prior to it.
The Seder meal had added rituals. Its four cups of wine are a talmudic legacy. After the Temple was destroyed many of its Passover rituals, except for the paschal lamb, were transferred to the home service.
In the New Testament Yahshua instructs the disciples to prepare the Passover lamb and unleavened bread for the memorial service in the large upper room (Luke 22:7). This is the same observance Israel kept in Egypt when they killed, roasted, and ate a lamb and the unleavened bread that went with it.
As they were eating the lamb and bread, Yahshua stood up and gave them new symbols to be used to represent Him: the cup with the fruit of the vine for His blood and the unleavened bread to represent His body. They were NOT eating a regular meal prior to the formal Passover service. They were observing the Passover itself by eating the sacrificial lamb (Luke 22:15). It was all one observance and one activity.
Paul chastises the Greek-influenced Corinthians for having a fellowship meal at Passover (1Cor. 11:20-22).
The Companion Bible says this was a social meal. This custom was Greek and called for each to bring his own food, so the rich ate well while the poor did not. It also led to the exclusion of some.
Paul condemns this, saying they are destroying the spirit of the Passover by this prior meal (vv. 23-31).
The Bible is clear: the Passover is not a time for fellowship meals–not before or after.