[GAMEPLAY] Twitch - Venom Cask not applying stack of Deadly Venom on landing

EDIT: Updated with clip in first comment below.

Enemy champions standing at edge of, but within, the Venom Cask indicator when it first lands are slowed but do not always receive a stack of Deadly Venom.

The ability states that enemies struck when the cask first lands will receive a stack of Deadly Venom.

This can be seen at 6:12-13 of the linked match. Zyra is slowed, indicating she is within the cask area, but does not receive a stack of Deadly Venom.