Diamond Ore not generating

I find it hard to believe I'm just this unlucky but it could be bad luck. Now on my third world since 20w07a was introduced and I have found no diamond ore. The first world was started in the previous version and I had found diamonds, found none since 20w07a. Second world created in 20w07a - no diamond found. Third world created in 20w08a. No diamonds found. Multiple hours of mining between Y=5 and 12 on all including excavating entire chunks. All different seeds.