After additional observations, this has some relation to MC-129409. I did also include a screen capture of two blocks that are shown in which I am standing in and can breathe. (Note, somewhat enjoyable however as even with the turtle helmet, one must wait a really long time to be able to fully use most of this update in survival without cheats due to depths).
Additional note. I did not observe this behavior in past snapshots to my knowledge. This included 18w10b,c,d, 11a, 14a, 15a and 16a. It was all reset in 19b so I cannot comment on the previous snapshot release.
After additional observations, this has some relation to MC-129409. I did also include a screen capture of two blocks that are shown in which I am standing in and can breathe. (Note, somewhat enjoyable however as even with the turtle helmet, one must wait a really long time to be able to fully use most of this update in survival without cheats due to depths).