I'm not sure if I can see properly but there is considerable thinning on the the elbow area, and on the sides just below the backbone and in front of the hind legs, where the waist is? Elbows could be rubbing on something but I don't see how that side area would. That doesn't look like any shed I've seen. That doesn't even look like Oban when he lost all his guard hairs. That looks like both undercoat and guard hairs both are coming out. I think I'd be Vetting for a skin scraping to see if some kind of bacterial skin infection or yeast problem is causing that.
Me neither, no furminator. I'd probably strip the coat with it.