We have lived in our house for 6 yrs. Never had a problem. Everything is flowing nothing is backed up. We have new development going on behind us and past us. I don't know if this has anything to do with the sewer odor we have
Only in one bathroom. It seems worse under one sink then the other. When its cold it seems to start smelling. We are on city water but have sewage company.

I think you need to poor water to help the non-moving waste water move flow. I have had this same problem in our cabin and was able to take it away. I also poured clorox to help with the smell.
Benigna Marko

We have poured clorox several bottles down drain. Still comes back. We also check the stopper for rotten hair it's clean. P-trap is clean as can be. It is driving us crazy. We thought it had went away but it warmed up then here in North Louisiana we just got another cold front coming through & smell is back.