Warm Weather Smell...Again
If it's a sewer smell and you are sure that all of the traps have water in them, then it's likely a cracked / broken vent pipe, or a bad DIY addition where they didn't take the vent pipe all the way out through the roof (that happens more than it should because people don't want to end up with a leak in the roof). Call a better plumber. Look for one that does camera inspections, they can snake a long flexible video camera into your vent pipes and look for cracks, dead animals etc. There are also detectors that can "sniff" out odor, it's primarily methane gas and a chemical that is the result of fermentation of the sewage called Hydrogen Sulfide (H2S). Good plumbers have those detectors.