The number of stacks displayed when you enter Mount Maelstrom is doubled because there are two world bosses in that map. If you killed a boss and went from 4 to 5, you're actually at 3/4 and only need to kill one more world boss.
The generators have a buff named "Nigh Impervious" that has the description "Designed to resist damage from nearly any source; nearly."
Perhaps teamwork is required in a story mission about teamwork.