See attached screenshots. Happens in almost every ravine.
Also affects ravine ledges: Seed : 3854556177424684123 Coordinates : "-105 37 597"
Linked issues
is duplicated by
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Affects 18w10d
Can confirm in 18w19b.
Can confirm in 18w20a.
And in 18w20c.

shows up in some small places
This still seems to happen when a regular cave intersects a trench. To find floating blocks created by regular caves and a trench, use the seed 6305367952379995540 and teleport to 955 12 -1521 and you will see floating blocks created by regular caves.
Still happening (when regular caves intersect a trench) in 1.13-pre10. See the seed and coordinates in my previous comment to reproduce for 1.13-pre10.
Edit: I also put a screenshot of the issue with F3 turned on to show the version. The caves that generated through the ravine were dry.
Still happens in 18w30a
Still happens in 18w30b
Still happens in 18w31a

Affects 18w32a
Affects 1.13.1
Affects 1.13.2 and 18w43b
Affects 18w44a
Affects 18w47a
Still in 18w50a
Affects 19w07a
Affects 19w09a
Affects 19w13b
Affects 19w14a
Affects 1.14 Pre-Release 1
Affects 1.14 Pre-Release 2
Affects 1.14 Pre-Release 5
Affects 1.14 and 1.14.1 Pre-Release 2
Affects 20w12a
Can confirm in 21w03a.
Can confirm in 21w05a. This can be seen in almost every underwater ravine.
Underwater caves no longer exist and have been replaced by aquifiers. Closed as invalid.
Affects 18w09a