Even if the enemy have infinity init and you have 0, their 4th won't go before your first. At least not as a result of init.

There are a few reason why this might happen:

1. You actually cast it late--this can happen if you do not cast at begin of round ASAP, even 0.5 second of hesitation might cost you. As for middle of round... cast delay is really complicated due to lag. Generally, if you do not cast at the START of the previous action sequence, you will be late. This is why I have to turn on auto sometimes during fights to have my gated mystery cast ASAP (I'm a dancing wind main w/ natural draining, so I have both mystery gated by chakra gain from natural draining chase, which will certainly be behind lag wall if I do manually, as well as mystery reset by wind main, which sometimes does)

2. Your mystery is not prompt.

3. Your team is slowed, see kurotsuchi