User blog comment:IamJakuhoRaikoben/Chapter 468: Memory of the Stars, Review./@comment-180.191.135.57-20160110011912/@comment-7418318-20160110091942

In the chapter they outright said that the GMG Eclipse went haywire exactly because there wasn't a controlling mage on each end of the time-tunnel.

If you think about it, there wasn't just a CSM missing in the past, but in the present too, since Hisui just unlocked the Gate with the keys, but didn't actually do any controlling. She just more-or-less flipped the doors open and let the fates decide the course of events.