Two diamond blocks in a row did not drop diamond ore (or anything else). I used a fortune 3/efficiency 4 golden pickaxe (found from a ruined portal) in some deepslate diamonds found in a cave.

Seed: -1363170156779338662

easy/survival mode

coords on one diamond ore: -756, -4, 864

I can't find out how to get my world file (from external storage), so hopefully I've given enough information. Let me know.