Can someone explain the mounting instant fail?

so I know about para making mount fail, I have mounted and para'd on the same hit lol...

but I was mounting a hyper tetsu just before, and doing good; 1/3 of the entire bar was green, I was almost done, then bam. instant fail.

This seems to be also similar to the ones where I mount, and the bar is instantly red; no chance to do anything. Can someone explain this?