I'm having a little bit of a problem with my pyramid model

So I just made this pyramid… But,
When I hit Ctrl+N to adjust normal a face under my second stairs disappear, like this

What am I having this problem and how did this happen?

this is how it looks like if I flip the normal of that face

the face is showing up if I Flip the normal inward.
should I keep it that way or this is going to mess up my pyramid?

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