Not sure if there is a form I need to fill in, so I'll just report it like this:

When you place two vertical slabs against eachother and then try to mine them, the block drops for a second and then disappears. The game then acts like the vertical slabs weren't mined at all, but they show up invisible. When you try to mine the invisible vertical slabs, the game crashes. I'm using Forge 1.19.2 version 43.2.1 and Double Slabs 1.19 version 6.1.0.