Unfortunately The feces odour problem seems to be a mystery problem . I suspect it can be caused by a variety of reasons .
I had it and found what was causing it for me was that I was under stress and was (without knowing it ) pushing my stomach out .
What I worked out with my body is that my sphincter by reflex is connected to my stomach muscles ie if I push my stomach muscles out my sphincter will push out and if I pull my stomach muscles in my sphincter will pull in.
With my body I also found out that if I have a quick deep breath my sphincter will contract in. I suspect this is how the sphincter muscle gets exercise naturally without you having to consciously exercise it to keep it taught.
One of the problems of pushing your stomach muscle out is you can only breathe shallow breaths so your sphincter does not get any exercise to keep it taught
I made a post on here a few days which explains what worked for me in more detail
I urge you to check your stomach muscles and see if you are forcing them out as this might the cause of your problem
Best of luck . I hope things improve in your life for you.
Let me know if you are pushing , tensing your stomach out and if you are I will tell you in more detail what worked for me
Ps I work in the country so please be patient in the time I take to reply