So I tried to make a custom block and I'm having some trouble. I tried to have it override the bed so I could have a couch instead of a bed. Now that didn't work, but I wanted to see if I could get it in the game at all, so I had it override the anvil. That worked, but the texture isn't loading at all, I'm not sure why, but it's frustrating.
Could you share all of your .json files (including the ones that tell where to find the texture), and the file path? This looks like one of them is not set up correctly, or tells minecraft to look in the wrong place.