I've placed the Dark Oak Vertical Slabs on the West, South, East, and North surfaces, and the clipping isn't working properly on the blocks below them, only on the slabs I place while facing West or North.

I'm going to include stairs in the screenshot to help show the issue a bit more.

Facing West:

Facing South:

Facing East:

Facing North:

I'll include one more image. This one, I'm facing North:

I'm not going to include the log for now (because I don't think it's necessary), but let me know if it could be useful and I will.

Not reproducible in 1.16.5 r2.4-311