Why do some items not show up on the app?

How come some items can’t be found on the app (Android app specifically), but can be found via the browser?
Here is an example: Corn Snack – Earth Control
I’ve seen this issue on many different items.

Question: do the items you’re talking about have one thing in common: lack of product photos, or at least lack of packaging front photo?

I think so, yes.
And since posting this, I’ve now updated a few items via browser and observed that simply adding an image is enough to get it to show up on the app, so I can complete it there.