Garen ult broken since 5.8?

Just played Garen for the first time since 5.8, and experienced an issue where his ult would start to cast (R has been pressed, animation of diving with sword has went off)... but then no light animation, no damage dealt, no cooldown triggered. This happened at least 6x over the course of the game.

I only managed to land his ult once during a 30 min game. It seemed that if a champ went out of melee range - Leesin could use a speed boost to run out of range mid-cast, Annie several times just walked away from me when the animation started - the animation would just stop prior to damage being dealt. Previously, once cast, even if a champ flashed, the light would follow and then deal damage. There were no items in play that would have negated the ability.

Intentional undocumented change, or is something broken here?