EX Mantis Slashes - only four hits?

Every once in a while when I do EX Mantis Slashes, I only get four hits off of it, even though I connect with the first slash and get the knockdown hit at the end. Any reason why this is?

You’re getting one less hit because I think you’re spamming on the EX slashes way too fast. I think it’s the first set of EX slashes that are getting cancelled.

O_O Holy crap i have the exact same problem. Sometimes the slashes get cut off even earlier…gotta stop spamming.