User blog comment:IamJakuhoRaikoben/Chapter 497: The Winter Mage, Review./@comment-122.180.163.221-20160809101355/@comment-24367018-20160809211230

A double issue means that the magazine it's published in covers this week and next week, which means that 497 is the sole chapter for the fortnight. That's what is meant by a double issue, not two chapters per series.