Currently miracle is extremely hard to obtain, especially since harder instances and dungeons don't really allow for the amount of mobbing to be able to get the buff properly. And it's extremely easy to lose.
To obtain it, you have an extremely low chance when dealing any damage to trigger this effect. And if you log off or change maps you lose the buff.
I propose two changes:
Increase miracle odds of being triggered by 10x for normal maps or dungeons. For instances there could be a different rate considering you'll spend little time there.
Make it so that if you ever get kicked out of the map, you have a timer of something like 1 or 2 minutes to allow you to get back into the map and regaining the buff before it goes away. This should help make it more consistent. The timer itself wouldn't provide the buff, just allow you to get back to the map before losing the buff.