Superior Sigil of Demon Summoning
I have that on one toon and it has worked in the past. I haven’t played that lately, though.
Try unequipping and re-equipping to see if that helps? Otherwise, sounds like a bug.
Sometimes if a person has another stacking sigil, such as bloodlust, it interferes with the Demon Summoning stack.
Be careful what you ask for
ANet may give it to you.
ANet may give it to you.