Why has my photo not appeared in the gallery?

A newly saved photo is prepared and checked before it is shown, and on some events the host reviews everything first.

A photo does not go straight onto the wall. After you save it, three things happen in order, and it appears only at the end:

1. It is cleaned up — camera metadata including any location is stripped out, the rotation is baked in, and smaller versions are made for the grid.
2. It is checked for anything that must not be published.
3. It is published — unless the host has switched on Require approval, in which case it waits in their review queue until they publish it themselves.

Normally this is seconds. If it has been much longer, the host has almost certainly turned on approval — they can see your photo, and it appears the moment they tap approve.

The other possibility is that you turned off “Make photo public” for that batch, in which case the photo went to the host rather than to the gallery, and is working exactly as asked.