The bug
Vines can grow under trapdoors, but then break again after some time.
It is not clear what the intended behavior is, also considering MC-117008.
How to reproduce
Place a lower trapdoor
Place a vine on the block below it
Increase
randomTickSpeed
/gamerule randomTickSpeed 10000
❌ The vine grows on the undersite of the trapdoor, and then breaks after some time
Can't reproduce. Maybe it was fixed by MC-113809?