I died while being on a ladder and the gravestone never spawned.
I would expect the gravestone to replace the ladder instead, but it would seem like the ladder got "priority" and the gravestone didn't spawned at all... And i looked everywhere with spectator mode.

GAME VERSION: 1.19.1

VERSION: gravestone-1.19.1-1.0.0

FORGE: forge-1.19.1-42.0.9-installer

Edit: The gravestone spawned at the very top of the ladder, and i read it on the faq part before posting this, but because it's a very big structure i couldn't see it in the first place. I do apologize.