I was going to kill Striders and so went to kill the striders in the lava flowing downwards, I hit them and knocked them back however they do not fall, they can either be pushed or hit out of the lava and this will happen, punching them in this state of floating in the air doesn't make them fall. Haven't been able to recreate it.

Edit: Managed to recreate it, Striders have weird interaction with blocks and lava when interacted with.