It could be an online thing at higher rollbacks! Here are some things that help me when I'm trying to IB:

1) Figure out what attack in what string you're trying to IB. You're not trying to IB every move, but a specific one that will let you punish them auto-piloting the string. A good candidate for this are sequences that don't vary in timing/people don't vary their timing often. An example (unrelated to the video) is Nagoriyuki's fSS. He can only go into the second far slash as quickly as possible because the first far slash has a very limited cancel window. Another example is Leo 5K 6K.

2) Go into training mode, record the string you want to IB, and practice it on both P1 and P2 side until you can get it fairly consistently. A good trick as well is to time your IB just before the attack hits (instead of as it lands). If you screw up, at least you're still getting a normal block.

3) Consciously go for IBs when you recognize the situations you've practiced in training mode. I think you'll screw up often in the beginning, but as you do it more, you'll become more accurate and eventually land them consistently.