Confirming the issue persists in 1.13.1
I downloaded 1.13.1-pre 1 and the issue is NOT resolved.
So far I have identified 20 separate bug reports raised over the past month, and all Mojang does is mark them as "resolved" and move on.
THEY ARE NOT RESOLVED. It also seriously screws up the game. What do we need to do to get Mojang to pay attention to this?
I tested it over 20 times. Generating a world in Creative/Cheat mode ALWAYS generates the structure. Survival is about 50/50.
-955523361464072251 is my test seed (A woodland mansion should appear at -450 320 )