This happens to me too.
But I should add that this only happens between the player model and the camera:
from behind: every slime block behind the player
from the front: every slime block in fron of the player.
ok thank you
Sorry, couldn't find my old post so I thought something happend to it...
Well what if you landed on a solid non bouncable block besides the slime block and you just hit the slime block by 10%, then you will not be bouncing, and the same thing happens when there is a non solid block or even air there. I do think that it should be improved when they have non solid block on the side.