Ore veins are overwritten with Deepslate during world generation. Naturally this affects mainly Iron Ore veins. This is major issue IMO, because ore veins are one of the greatest things made with new generation, so losing iron veins is very sad for Minecraft.

This started happening in 21w44a, and there badlands/wooded badlands had no deepslate, and I could see its Stone <0 part had an iron vein in one of the worlds, then its part where in was intersecting into another biome which had Deepslate was cut immediately.

To reproduce (may need X-Ray to see things):

1. Do not change vanilla noise settings, create single "the Void" biome world using seed "1". Go to coordinates 200:40:120. Copper ore vein present there. Go to coordinates 125:-35:-125. Iron ore vein is not there.

2. Change "overworld.json" in vanilla noise settings, removing deepslate generation part. Create single "the Void" biome world using seed "1". Go to coordinates 200:40:120. Copper ore vein present there. Go to coordinates 125:-35:-125. Iron ore vein present there.

3. Change "overworld.json" in vanilla noise settings, elevating deepslate generation part (e.g to 40 to 48). Create single "the Void" biome world using seed "1". Go to coordinates 200:40:120. Copper ore vein should either be removed entirely or exist on positions not replaced by Deepslate, depending how high you've lifted that Deepslate. Go to coordinates 125:-35:-125. Iron ore vein is not there. Started happening when "deepslate_enabled:true" in noise_settings was replaced with manual deepslate generation part later in file. Happens up to 118-pre2.