That's totally normal. Ball pythons are known to go on hunger strikes for up to a year. Personally, I think it's because most are overfed, or at least fed much more than they would get in the wild. So unless he starts losing significant weight it shouldn't be a problem. If you can add a picture of him that would help to check his body condition. I think your feeding schedule sounds good so I don't think there's a problem, just one of the perks of having a ball python, lol.