I haven’t had this issue (yet). Looks like you’ve used all tips and tricks. This is what I found directly on their website:
Q: Do the bags absorb smells?
A: Stasher silicone is nonporous, inhibiting bacterial growth and odors. Certain smelly foods may leave a slight odor in the bag, but that can be remedied with a thorough washing or baking soda soaking. A fresh slice of lemon left in overnight can help too.
Have you tried leaving the lemon in the bag overnight?