The game Star Trek timelines has boss battles against the Planet Killer (AKA "The Doomsday Machine" from TOS). It needs to be attacked by several players from the fleet to be destroyed, and even then the damage is minimal. But I can do more damage with the "Combo chain", the characters selected for the attacking ship. See an example here (the screenshot is just an example to help with the explanation)
Garak, Archer, Bashir, and Khan are 4 of the 5 characters that have been added to the combo. To unlock it and do great damage, I would need to unlock the 5º one. That means, a character who is human and has 2 other traits from the list below. Problem is, when I do that sometimes the character is added to the combo, but in most cases it is not, even when the mandatory and secondary traits are all there. Clearly there's some other rule I fail to figure out.

Garak, Archer, Bashir, and Khan are 4 of the 5 characters that have been added to the combo. To unlock it and do great damage, I would need to unlock the 5º one. That means, a character who is human and has 2 other traits from the list below. Problem is, when I do that sometimes the character is added to the combo, but in most cases it is not, even when the mandatory and secondary traits are all there. Clearly there's some other rule I fail to figure out.