Warrior action "Infuriate" sometimes does not become available when hunting S-ranks

Date & Time: 20/07/2017, approx 11:30 PM CEST
Frequency: Twice around the time listed above in two separate S-ranks
World name: Balmung
Character name: Lleidileita Mhaswyn
Retainer name: N/A
NPC name: N/A
Monster name: "Gamma", in Yanxia and "Bone Crawler", in The Peaks
Class/Level: Warrior, level 70
Party or solo: Party, plus many out of-party players
In-game time:
Area and coordinates: Yanxia, The Peaks
Housing:
Steps:
1. An S-rank was called while my party was in the area, so we detoured to fight it.
2. We get there, the fight has started, and I dismount the chocobo and start fighting.
3. After about 5 seconds I realise that "Infuriate" is still grayed out like I was not in either Deliverance or Defiance
4. I took a screenshot of it happening, to show I was in deliverance; but I notice now that the monster was not on my Enemy List, so perhaps the warrior ability did not trigger because I was somehow not in combat.
http://i.imgur.com/OcEF3Dc.jpg

Connection Specs
- Type of internet connection/provider: Cable 50/25mb
- Modem maker/model number: canal digital

I noticed a delay, but it always activates. Though I learned that its better to double tap your keybind.

That was not true for me in either instance. It stayed grayed out for the entirety of two fights. Worked as normal when I attacked a normal mob a bit later.

This is a behavior that's mostly present when there's a lot of players attacking the same creature. Someone on reddit had a theory that there's a 'cap' to the number of players that a mob can have enmity registered for and anyone that's not high enough on aggro is 'ignored' and considered not in combat to that enemy. I've had the same thing happen, but the instant I get a single butcher's off on any S-rank or ixion in Defiance, Infuriate instantly lights up, leading me to believe it might be the reason, if not related.

Either way, it seems to only be an issue during S-ranks or Ixion.