Cooldowns set to items like ender pearls aren't updating the hotbar.
Note that custom servers can set the cooldown for any item type.

Good point. Will fix that together with the enchant glint(kinda forgot about that too).

Item animtions don't work well in hotbar (as the cooldown)
I think it's the same problem ( and I'm lazy to open new one )

Already fixed in the latest commit, forgot to close this.

I tried this build
By my test, to let it works well, you need to let it buffer once after something start cooldown.

What do you mean? That build refreshes at the settings fps as long as you have a cooldown active or enchanted item in the hotbar.

This BUG doesn't fixed completely.
It doesn't refresh automatically.