Flask Enchants in Trialmaster Boss Fight

They simply didn't work, that's all. Both "Reused at the end of this Flask's effect" and "Used when Charges reach full" doing nothing when I encounter Trialmaster on his arena, and I didn't take "Drought" Ultimatum modifier (even if so, the "Reused at the end of this Flask's effect" didn't work when Flasks have enough Charges to reuse the Flask).