It is strange that in the deepslate level, that dungeons would still generate with cobblestone.
Steps to reproduce:
1. Find a dungeon under y=0
2. See that it is cobble
What should happen:
It should be made of cobbled deepslate rather than cobblestone under y=0
This is not a bug. They have not added that to the game, what you’re describing is adding a new feature. Go to minecraftfeedback.com to suggest this