I have been experiencing an unusal problem with vertical pipes.
Sometimes she circle shown in detail level: medium. disapears ! Only when the pipe is connected on both ends.
I've found to work, to change the pipe type, then the circle appears, even though its changed back to previous type.
See in the red circle, and # labeled. No difference between those two pipes (exept the obvious, other one is not appearing)

Btw.
Both pipes are 100% vertical - already checked about a thousand times.