It is a number of Hunters problem rather than a mechanics problem for most of the hunts. To many hunters end up killing the marks before all of their signatures become visible.

Did you know Zaniq'oh deals retributive damage when it is glowing purple?
Did you know Hellsclaw will reflect either Physical or Magical damage for a short period after it uses Counter Maneuvers?
You probably know that Sabotender Bailarina can instant kill anyone caught in its 20k Needles AoE.
Both Alectyron and Maahes have large AoE Petrification and Paralysis abilities and Alectyron can also inflict Sleep.

Pretty much every A and S rank is a decent fight with fairly decent mechanics if you face them with group their expected party sizes, but they get swarmed by groups of 5 to 10 times as many people.