False structure generation

So i loaded up a world in the snapshot 23w14a and i found an igloo with a trapdoor in it. But there was no way down and when i looked down with spectator mode there also was no structure generated.

What I expected to happen was...:
I thought every igloo with a trapdoor has this structure underground

What actually happened was...:
I broke the carpet and opened the trapdoor but i didn't find any underground structure

Steps to Reproduce:
1. Find an igloo
2. Break the carpet
3. If it has a trapdoor in it look if there is a underground structure and else you should check it to, to prevent other bugs