This problem was originally reported in 1.17.0. It was fixed in 1.17.2, but as is usually true for world generation bugs, the fix only affects new chunk generation. It is therefore expected that chunks generated prior to 1.17.2 will continue to show incorrect distribution of ores (diamond and other). Please try not to report any further examples of the bug in those chunks.

Nevertheless, we are still receiving new reports that might indicate a similar problem still occurs after the 1.17.2 fix, and we're using this ticket to gather information. We need your help as follows:

1. Make sure the problem you're seeing isn't the result if old pre-1.17.2 chunks. If you're not sure, try creating a new world with the same seed, then compare ores at the same coordinates, If the blocks are identical, then it definitely isn't old chunks.
2. Make sure that it's not just a normal variation. If your example differs in degree (fewer or more than expected) instead of kind (found ore where there shouldn't be any, or vice versa), it would be a good idea to mine a bit more, maybe in a different direction, to see if it's widespread. It's impossible to be 100% certain, but the larger the affected area is, the more convincing your example will be.
3. Once you have a convincing example, be sure and tell us the world seed and where in the world you saw the problem (coordinates of the location, size, and direction would be perfect). Also very important, we need to know whether you have the Caves & Cliffs Experimental toggle turned on in the world settings, as that completely changes the rules for where ores should generate. If you prefer, you can upload a copy of your world and tell us where you were mining.

If we're able to get a couple of reliable examples, we'll submit this as a new bug to the developers. Otherwise, we'll eventually have to conclude that the bug is already fixed and subsequent reports are just cases of old chunks that can't be corrected.