Curled Waxy Dark Green Blackberry Leaves

I have seen curled waxy dark green leaves on some of my blackberry plants like the photo below. Does anyone know the issue and how to resolve it?

i actually noticed that on a few of mine a month or two ago, I wasn’t sure if I had finally caught a blackberry virus from mixing so many varieties together, or if it was from the type of fertilizer i had just hit it with - mine were curling in a spiral too