I can see a few sorts of issues that suggest you made some early oopses and then went astray attempting to fix them.
You have created some peculiar and excessive nesting of groups and/or components. For example, the Small Foot Stretcher component has four groups in it that all duplicate the same set of edges and faces. In that same component there is a group that nests a component named “bottom” that contains just edges. Nearly all of your components and groups show this kind of over-complicated and redundant structure.
The excessive nesting and duplication can make it confusing just what you have open for edit. I suspect you have been trying to create faces using some edges from “bottom” and other edges from the other nested groups. That won’t work! All the edges bounding a face have to be in the same group or component as the face.
At the upper right corners of the “Another Leg” component (or maybe the “New Leg” component nested in it), there are some tiny mismatches between the edges that become visible if you zoom way in. They wreak havoc when you try to complete faces because unless zoomed way in you don’t know which one of the possible vertices the inference engine may snap to. All the edges must be coplanar before a face can form, and that is hard to assure when there are multiple end points so close together.
There are also places where edges are not coplanar. You can search for these by drawing diagonal edges across where you thought should be a face. If two triangles fill in but disappear when you erase the diagonal, the other corners are not coplanar. For example, on the side of the small foot stretcher:
I’d start by exploding the duplicate nested groups until you get all connected edges and faces into the same edit context. Then try some diagonals to check for coplanar. Finally, if diagonals won’t create faces, zoom in very carefully and closely and look for extra spurious edges that don’t quite meet. Determine which are correct and delete the rest, redrawing some if necessary and being very careful about waiting for inference snaps before you click to start or end an edge.