My iron pickaxe was about to break, so I crafted a new one. The new one showed the same green level as the old one. Both axes ended up breaking after a couple of hits. Could it be because I paused the game while I made the pickaxe? The old pickaxe was in my hotbar and then I swapped the one in my hotbar with the new one from my inventory. I am not 100% sure if the new one already showed a low green bar before the swap or not.