Tactician Supporting Fire not working at Trial Master encounter

Hi, I thought I was doing something wrong at first, but it occurs every time.
I can run the trials of Chaos using the Command:Death from above as my main skill, works on all encounters - but when i get to the trial master the skill will not work.
the skill icon greys out. the other minion command skills work, but Supporting fire will not.

this effectively stops me from farming the trial master on this character as the bulk of my damage comes from this skill.

this does work in Sekhama's