Filled faces doesn't show up in UV mapping

I recently discovered that filled faces doesn’t show up in UV mapping, even though the rest of the object shows up correctly. I’ve not been able to find a solution to this or other topics similar to this.
Is there a way to fix this?

I think they are showing up: see black dot at lower left corner (under cursor)?
Not sure what the correct way of doing this, but I suppose you could pin the rest of the object (with P in UV Editor) and then press Unwrap to unwrap these new faces.

The pinning and unwrapping did wonders, Thank you!