Does anyone have a rabbit that over grooms?

I have been reading about this all afternoon. We have a mini lop and he excessively grooms to the point that he is missing fur on his legs. We have consulted our very rabbit savvy vet, and she said she thought it was due to his discomfort with his arthritis. He is on daily pain meds (Metacam). But, we are noticing he is still grooming these same areas, and we have noticed another new area is being groomed. Our vet has shown no concern because there are no other symptoms or signs of anything. So, the only thing I came up with was that it could still be a sign of pain or it could be behavioral/psychological. He is 6 years old, and we are wondering if he is bored, but we have tried toys and other things that he could interact with, and he has shown no interest. He has a huge cage, and we let him out frequently to explore, but we have to close his cage off because he will just run back and refuse to come back out. I'm not overly concerned at this point, but I am worried about how much fur he is removing from the excessive grooming. Any ideas what can be done? Should we consider asking the vet about increasing his pain dosage?

Where exactly and how much hair loss are we talking about here? It can take a while for the hair to grow back. Are you seeing him groom still?
There's definitely the possibility that this started due to something like arthritis and developed into a learned behavior that he just does now. I'd also consider some dermatologic testing to help rule out a pyoderma (skin infection) in that area or ectoparasites.

It's on his back legs primarily, in a section of maybe an inch and a half? I have seen a new small patch on the front of one of his legs, but mostly it's confined to the back legs around the hip area. From what we can gather, with the knowledge from our very rabbit savvy vet, he was dropped or injured before we got him. She did some testing and really believes it's arthritis, but we were concerned about how much hair is missing and how he continues to lick it. There is nothing there that we can see. It's just bare skin and the fur around it is kind of tangled from his excessive licking. The skin is not irritated or anything. I can ask for dermatological testing, but our vet really didn't think it was necessary. I was wondering if it could be behavioral and if I could find a way to stop him from being so excessive about it.

If it's behavioral, it could be because he's bored. Do you have any toys with him for while you are gone? I have one rabbit who is too smart and we have to keep coming up with things for him to do, maybe yours is the same way?

We hide pellets in puzzle toys for him to find and figure out. Sometimes we have to get pretty creative. One of my favorites is to stuff a toilet paper tube (just the cardboard part) with hay and a few pellets and fold the ends in on each other. It takes our bunnies a while to get them open and find the pellets, keeping them busy for a while.