MC 1.17.1
Fabric API 0.41.0
Continuity 1.0.1
MineGate 1.1.6 Not necessary, see comment below.
NAPP 3.5 (tested with 3.4 too)

1. Install Continuity, MineGate and NAPP
2. Activate only NAPP texture pack
3. Place vertical stairs from the MineGate mod in such a way where you can see the bottom part of it, or place vanilla stairs upside down in a corner

With Continuity 1.0.0 and 1.0.1 build10, everything appears as intended. But with Continuity 1.0.1 release, the bottom part is culled. I didn't test with other texture packs, so it might be a problem with NAPP, again, but since it didn't happen on previous versions on Continuity, I figured I'd report it here.

That's how it looks with 1.0.1 release: [removed]

That's how it should be and how it used to look with 1.0.0 and 1.0.1 build 10: [removed]

Actually, the issue happens with vanilla stairs placed upside down in a corner, so MineGate has nothing to do with it, it was just easier to spot.

I forgot to add a single line when I replaced the culling code, which causes only the first quad on a cull face to cull correctly and the rest to always cull. Sorry about that. I'll try to fix this and release 1.0.2 today.

This should be fixed with commit af05590. I will do a full release as well, since this is a critical bug.