Seems like the rng is seeded based on something in the group.

Running with the same 4-man hm group every day for the past three weeks, here are our drops :

Maelstrom Prison : Jedi Councilor Boots

Battle of Ilum : Commando Off-hand

False Emperor : Smuggler chest

Rise of the Rakghouls : Jedi Knight head (bonus boss), Jedi Councilor head (final boss)

False Emp we've run about a dozen times, and only twice did we not see the smuggler chest (both times it was the commando one). Maelstrom Prison we've run three times, Battle of Ilum we've run three times, Rise we've run twice (but saw identical loot off of both bosses).

Random is random? Probabilities for these strings assuming uniform distribution on the four tokens...

Maelstrom Prison : 3 runs, probability of all three being the same is 1/16

Battle of Ilum : 3 runs, probability of all three being the same 1/16

False Emperor : 12 runs, 10 out of 12 were the same, probability is 0.00015 ("high" estimate, 4 * bindist(0.25, 12, 10) -- does not account for two failures being the same)

Rise of the Rakghouls : 2 runs with 2 drops each, probability is 1/16

Based on other threads on this subject, it seems like going with different groups will give you different drops, so it might be something silly like the rng used for loot drops is being seeded with something static in the group.