It’s annoyingly inconsistent assassin behaviour that’s been part of the game forever AFAIK.
Assassins sometimes decide to bounce off of a wall and it’s hard to predict if it will even happen in the first place much less react to it. They just stay in the air in their pounce as they slowly turn to face you without touching the ground.
Fun fact: this happened twice in a row in 2 back-to-back games both of which resulted in a wipe.
