Sure thing, I'll try to make this as simple as possible. Here Is a simple pack I made using the Blockbench wizard. The tool (test) mines the block (test_block) perfectly. However, no durability gets lost. Attacking mobs with the tool, however, does take durability points away.
I honestly am also starting to doubt that this is 100% fixed, but I can't say for sure. I did some tests of my own and I can confirm that the diamond ore generation is definitely better, but I think I'm gonna have to come up with a new method of finding and mining them.
I think I discovered another way to avoid this. It seems like minecraft launches faster and bypasses this glitch whenever you don't have an internet connection. So i usually disconnect from the internet before I launch the game. But that means you won't have access to the marketplace even of you reconnect. If you want to go shopping, then you must launch the game with an internet connection. But i'm not sure if this is fullproof though.
Yes. It even says that the pack is missing when I launch the game.
Please note that I'm fairly new to modding and mostly use Blockbench's wizard to make things. You can also reproduce the issue by simply making a tool and block for the tool to mine on Blockbench (or assign the tool to mine base game blocks), and you will see no durability gets taken. Maybe the Blockbench plugin/wizard needs to be updated?