Question about Chapter 4 - the chapter in which 6 mice split up into two groups.

After the split, when one group explores a new room, does the entire initiative track get reshuffled including the mice and minions in the other room?

Or do you keep the initiative track the same and always add new encounter monsters to the bottom?

Or, do you shuffle each group's initiative cards separately, perhaps by dividing the initiative track in half and keeping track of each separately, and do each team's reshuffle upon entering a new room as per the rules?