Rek'Sai Ult Unreliable

Okay so I built a hyper carry reksai. She destroyed quite well except for her major thing: her ultimate, it doesn't knock up everyone adjacent which would be more like her burrow in game and she also doesn't knock up at all sometimes. If a champion moves who she is targetting for burrow she goes to where the enemy was not where they are, which is ridiculous its not a skillshot its a champion moving, it should be able to move to a spot where a champion is even if they moved. Sometimes champions will just sit still too.

What her ult should do is burrow, go to an enemy champion and knock up any champion in the surrounding space of reksai, I've literally been circled by 6 people and not knocked up a single one of them as reksai... not even one. It's ridiculous how unreliable it is.