JapanMS - Patch 1.82 Highlights

Regarding Chains of Hell, it deals the damage of 24 hits, but only 15 are shown. This is what i believe it does.
It's like JellyFlower said, there's a cap on how many hits are shown. But what you see isn't what happens. That level 186 Raika video is an example, the damage he deals is so huge, that only 15 hits wouldn't be enough to deal such a high damage.

You wouldn't even be able to notice the difference in time. It's not like 9 MI hits do a lot of damage.