User blog comment:B214/Question and Answers 3/@comment-108.27.243.235-20140719235241/@comment-23853100-20140720005708

bribing issei back to life. +___+

And it was mentioned that his ability became unstable in Volume 14 without Ddraig. While in Volume 17, Ddraig only went to the Divine Dividing's SG depth, he wasn't sleeping like in Volume 14, so he may have made sure that Issei could use his SG.