Trust: Robel-Akbel will occasionally refuse to cast spells.
Platform: Windows
ISP: BT
Type of Internet Connection: ADSL
Internet Connection Speed: 1Mbps
Date & Time: First attempted 11/08/15, since then consistently.
Frequency: Always
Character Name: Jeral
Race: Hume M
World: Phoenix
Main Job: SMN
Support Job: RDM
Area and Coordinates: Ra'Kaznar Inner Court (F-9), all areas along the bottom half of the map
Party or Solo: Solo, with Trust x4 (Yoran-Oran [UC], Kupofried, Qultada, Robel-Akbel)
NPC Name: Robel-Akbel trust
Monster Name: Boilridden Umbril
Steps:
Test 1:
1. Locate a Boilridden Umbril.
2. Using item level 119 equipment, use the check function.
3. Engage in combat with the Umbril.
4. If the monster checked as "Tough", Robel-Akbel will occasionally cast spells.
5. If the monster checked as "Very Tough", Robel-Akbel will never cast any spells.
Test 2:
1. Locate a Boilridden Umbril.
2. Using item level 119 equipment, use the check function.
3. Engage in combat with the Umbril.
4. If the monster checked as "Tough", Robel-Akbel will occasionally cast spells.
5. If the monster checked as "Very Tough", Robel-Akbel will never cast any spells.
6. Use Ifrit's "Conflag Strike" Blood Pact ability upon the Umbril.
7. For "Tough" monsters, even if Robel-Akbel did not initially cast any spells, he will now consistently cast spells.
8. For "Very Tough" monsters, Robel-Akbel will still never cast spells.
Test 3:
1. Locate a Boilridden Umbril.
2. Using item level 119 equipment, use the check function.
3. Engage in combat with the Umbril.
4. If the monster checked as "Tough", Robel-Akbel will sometimes cast spells.
5. If the monster checked as "Very Tough", Robel-Akbel will never cast any spells.
6. Use Ifrit's "Meteor Strike" Blood Pact ability upon the Umbril.
7. Robel-Akbel's spellcasting behaviour will not change.
Theory:
This reminds me of the issue automatons used to face when using a scanner attachment. Robel-Akbel appears to favour casting spells of an element that the Umbril is weak to - generally Fire-based. Perhaps the Very Tough mobs are too strong for Robel-Akbel to be able to discern a relative weakness?
Using Conflag Strike would always be enough to force Robel-Akbel to always cast spells on Tough umbril, but never Very Tough umbril. The Burn effect of Conflag Strike reduces the INT of the umbril, rendering it more succeptible to magic attacks. This would appear to support the idea that Robel-Akbel is not casting spells because the umbril are "too resistant". Meteor Strike, a similarly-powered attack that does not inflict Burn, does not have the same effect.
Just an idea. Hope it helps.