Flask Enchant "Used When Charges Reach Full" Not Working in Ultimatum Boss Encounter

I've been farming the Ultimatum boss for a while, with over 10 encounters, and four times I got randomly one-shot by the Trialmaster. Couldn't figure out why, but now I see that my 'Taste of Hate' isn't working (I use Mageblood, so this is the only flask I have with this enchant).

After entering the boss fight after round 10, even when I hit the flask and it fully recharges, the enchant still doesn't work.

Also, there's no Ultimatum mod messing with my flask I didn’t pick "Cannot Gain Flask Charges" and my flask still gains charge.

Edit: I've also tried it with the 'Reused at the end of this flask's effect' enchant, and this doesn't work either.

I am having the same problem, my flask was running when I entered the arena but it just didnt activate again even though I had the charges,

this has happened to me twice first time I thought I just didn't have my flask up due to it ending right as I hit the transition

since im running a wardloop build I immedietlly kill myself when my flask doesn't work, so rip getting the challenge I guess

As of the Necropolis league, this bug is still NOT fixed.
I hope GGG sees this and fixes it, just seems to be something that can be patched out easily...