(Bug) Might of the Guild (Mage Guild Passive) does NOTHING for Reflective Light (Templar Skill):

Mortosk

To Recreate Bug:

Casting Volcanic Rune to trigger Might of the Guild passive.
Notice Passive Icon indicating Might of the Guild buff is on.
Cast Reflective Light, record your damage (for my test it was 251).
Notice Passive Icon indicating Might of the Guild buff is off.
Cast Reflective Light again, and note the damage is the same (251 again).

The Damage of your next spell is supposed to be 10% higher (with 1/2 Might of the Guild), but it does nothing instead.

Akhratos

The damage of your next spell is not supposed to be 10% higher. The spell damage contribution for your next spell ability used is. Spell damage is only a part in the final ability damage done by magicka skills. The same stands for Weapon damage and stamina skills.

Now, If I recall correctly Volcanic Rune triggers the passive and consumes it so it gets the extra spell damage for itself when the rune denotates.

Try triggering the passive with Inner Light activation or Equilibrium for example, and try not using skills that do damage+dot because it only affects the first tick or activation damage and not the entire ability damage.

Also, take in mind that the server is not communicating in any way that you have triggered the passive. The addon you are using (FTC?) is "emulating" the buff timer when you use any skill from the mages guild, wich can cause false triggerings sometimes (I dont mean in this personal case, just to have it in mind when you test it).