Cresselia broke out of a Critical Capture?!

Question

I was SRing for a 4IV Cresselia a few days ago, and around Attempt #500,000 I got a Critical Capture. I threw the Poké Ball, she went into it, it shook in mid-air, and it fell to the ground. But before the ball even got the chance to shake, Cresselia broke out of the Poké Ball. On a Critical Capture! I thought those were supposed to guarentee a catch! Help?!

Comments

Attempt #500K
yes ofc :P

Answer 1

Critical captures drastically increase your chances of capturing the Pokemon, but if it doesn't shake once, it can break out. Good luck with your SRing!

Source: Same thing happened to me with Virizion in Black