Vanilla has this disabled as a kludge fix for MC-195461. Sodium could probably do a better job, re-enabling cullface for these blocks and fixing the original bug properly in the first place.

https://bugs.mojang.com/browse/MC-208189
https://bugs.mojang.com/browse/MC-226540

Thank you for the detailed issue, in particular describing vanilla's fix for MC-195461. It's not clear if the culling issue is still present in Sodium or not, I've been far too busy to test.

Regardless, this helps immensely figuring out how the issue was "fixed" in vanilla. Originally I wanted to make sure we mirrored vanilla behavior, but it seems like that isn't necessary

fYI, the above screenshot (as well as all my recent screenshots posted here) was taken with Sodium active.

Fix confirmed: