It maybe that you need to try to stretch and strengthen your feet.
When you run off road your feet need to be more responsive to the changing terrain. It is not going to be flat, your feet will often land at an angle, you'll hit stones and rocks. You'll slip and slide. Your using your body in a different way to the way you use it when you run on road.
Heavy mud is not nice to run in is it. It sticks to your shoes in great big cloying clods. It's slippery and uncomfortable to run in. You may well be doing things with your feet to try and stabilise yourself without realising it.
Give your feet a post run massage, stretch them out, wiggle your toes and rotate your ankles. Also flex your foot more.
Off road shoes don't have the same cushioning that road shoes have, they can't if they want to be responsive. You are taking more of the landing impact through your feet.
So long as nothing is amiss you should be alright.
