Yarus, Roar of the Old Gods - What triggers losing Haste?

Edgar

Yarus says when a creature with haste loses Haste, loses a reinforcement, or is destroyed, reinforce Yarus, then reinforce a Cloaked creature you control.

I'm playing with Tyvar Jubilant Brawler, whose abilities can give cast creatures haste until end of turn, whether in hand, or out of the graveyard. However, at the end of the turn, when they lose haste, Yarus' ability doesn't trigger, whether it's himself, or another.

What is the intended way of a creature losing haste other than at the end of the turn, or is it bugged?