J'ai fait une liste de peur qui'il n'y ait une problème. -- I made a list, for fear that there is a problem.

The y in that sentence comes from il y a, i.e., "there is".

In the subjunctive and with the required ne-explétif (because of de peur que), this becomes ,

il n'y ait.

I was puzzled there by the y in il n,y ait but Chris explained it very clearly. Thank you