Welcome to the Forum!

Here is a thread with some of my liner patching tips.

How deep and far around is the washed out vermiculite? (this will effect the viability of patching and the method used to patch.)

I'm thinking you might be able to patch the hole itself, then fill the dimple with sand and put a larger patch over the dimple and sand. (yeah, I foresee a couple possible issues with that, but it's a 'work in progress' )

Please keep us informed and we'll help as much as we can.