So I got some scented dish washer soap the other day and my wife used it the first time the other day in the dish washer including by sandwich container. Today when I eat my pb&j she made it tasted like scented soap. Do you think this is from left over water/soap or from it being scented soap?
It seems likely that there was some form of residue left behind in the container; whether this was actual soap or just the scent is difficult to determine. I have found that soap scents do tend to cling a bit more stubbornly to plastic than they do to other materials, but that's just my experience.
Next time you might try rinsing the container and drying it out with a clean towel after washing.
Alternatively, you might simply discontinue using this particular soap. It may be particularly clingy or perhaps you're just sensitive to its scent.
Concentrated dish soap can have a strong effect even if only a tiny bit entered the peanut butter jar. This is probably what occurred. To be safe you could take a clean, dry spoon and scrape off the affected layer of peanut butter, and discard. Provided it is only on the surface.
If the entire container is affected, it may be difficult to remove from the plastic. It may be best to use glass containers in the future if you plan on reusing containers; or if you use plastic, wash it by hand instead of going through the dish washer.