When I added some of the resource packs, I saw that some of the rail had the upward facing side incorrectly culled when Block State Culling is enabled.

Can you include the resource packs you where using?

@WinExp I would rather you send me it on discord if possible. At fx.morin

Probably not, this resource pack is a paid resource pack and sharing it requires the author's permission, which I don't have

I asked the author and he asked that the resource pack not be accessible to anyone else, can I send it to you via email?

the cullfaces of the model are set wrongly. basically "cullface": "direction" needs to be removed from elements which shouldn't be culled when that side is culled

But it looks like vanilla calculates whether the face is actually occluded or overlapping, so if moreculling does the same thing then shouldn't it have this problem?

This is kinda true, but not really. Vanilla just culls really inefficiently.
We may look into doing some optimizations for this later, however I wouldnt expect that any time soon.

vanilla just have canOcclude which is false for rails and a lot of other blocks. this is what happens if you set it to true for rails