Random air "pockets" found in the ocean

When traversing the ocean floor (thanks to Respiration and Depth Strider enchantments) you will find pockets of air, normally 2 blocks tall and 3 blocks long. I hadn't recently seen these in any other version. It looks like there were blocks there, but then removed, but won't fill in with water. I do not currently have a screenshot, one can be provided if needed.