8months after tennis elbow release surgery im feeling pain, stiffness in elbow. Cant twist my hand without pain. Hand and fingers getting numb. Why?

Nerve involvement . It's possible one of your nerves running through your elbow is being irritated or compressed. Could simply be from swelling or could be something else. Best to contact the doc who did the surgery.
May be a recurrence. Pts can have more pain despite the surgery. It is not necessariliy the same cause but the pain can be similar. The tennis elbow problem is actually a tendonitis. If you have resumed the same activity you need to go see your doctor.