No mods are installed.

I have a stone axe with:
Efficiency I
Unbreaking I

When I use it until it breaks, it doesn't shot on my hotkey bar. (3). I hear the tool break sound, and there is nothing in my hand. While using the empty slot, I only hit with my hand.

I take an unused stone axe, place it in my empty hand, and the old stone axe is thrown to the ground.

I can repeat the process 5 times until the axe breaks. On the last break, there is no sound for it to break, and it no longer reappears.