week three hot humid day sun bearing on the wall the smell came back must be in the plaster
It sounds like we're chasing the same thing (do you have a window involved?). I definitely think it is originating here, at least coming into the room, at the window. Please update if you figure out anything!!

You may have figured it out. It sounds like the odor might be the smell of rot coming out of the wall. Whatever caused the original rot that you repaired may still be allowing water into the wall still and the sun & heat may be bringing out the smell.
I'm thinking you are right (had not considered wood rot could smell so foul!), and hoping it is the actual sash and not in the walls (the stops and sides are not painted and have no rot like the sashes. Today with lower temp and less intense sun, the room was normal smelling, but I moved the sash and the odor seemed to escape only then). I so appreciate your input - this is quite frustrating!! Thanks!