Shower drain smell that no one can fix!

[rickwhoo]

That also looks like an exhaust fan vent in the soffit.
Probably from your bathroom.
Vents like that are a poor design, they should go out the roof.
The output from the exhaust fan vent just gets sucked back into the little vent openings in the soffit.

Might be a solid soffit without openings. I tried zooming in but couldn't see for sure...

 

[Jeff Handy]

Yes, it might be solid.
But some sewer stink could still rise into that exhaust fan opening and escape into the bathroom, if air pressure was lower in the house than outside.

 

[rickwhoo]

Yes, it might be solid.
But some sewer stink could still rise into that exhaust fan opening and escape into the bathroom, if air pressure was lower in the house than outside.

I do agree. And that vent pipe is in the wrong place...