Have you ever carried anything in the bag that would attract the attention of the dogs? Been to a concert where many people were smoking pot and the smell was on your clothing and now is in the bag? It's totally possible they are not picking on you, but for some reason the bag is flagged, and whoever picks up that bag is going to get screened.

If they come up to you right after you pick up the bag, I would consider it to be part of the issue.