When you scroll to switch between 2 slots of your hotbar with the same number of the same item, (ex. 64 white concrete in both of 2 bordering hotbar slots) the animation performed when you switch between hotbar slots will not play.

How to re-create:
-Put the same number of the same item in 2 hotbar slots that are next to each other.
-Start by selecting 1 of the 2 slots and use scrolling to switch to the other.

I expected to see the initial block go down and the one I was scrolling to come up. (The hotbar switching animation.)

I saw someone else attempt to report this issue but fail because people didn't know what the switching animation was and it was incomplete. Basically what I mean (similar to the last paragraph) is that when you use the scrolling function on your hotbar to select a different slot, the block you started on should go down on your hand and the new, selected block should rise up from your hand. I hope this makes it clearer.

Attempted to send video proof, but videos exceeded maximum file size.