Ball Pythons will and DO go off feed even when given the proper husbandry. Some when over fed will fast for months to catch up. Others will just fast as their at that size. You need to keep in mind that ball pythons in the wild barely eat 12 times a year let alone every week. So if everything is spot on with the setup then you have nothing to worry about. Stress is NEVER ALWAYS the cause for a snake to go off feed.