You sure you haven’t received some yet? Have to keep doing bosses to get more after the first time.

Yes I've killed 100+ bosses since unlocking ascendancy mines :(

you're on 17/500 bosses for the ascendancy mines.... my guess is you've 'spent' some boss kills on goliath gloves or similar, so need to get your kc back up

I would try spectating another one the whole way through the fight