I was trying to find my old post on this. I was not a competitive runner, but probably ran 3-4 miles, two or three times per week. After surgery and the six month recovery, I tried again. Invariably, a deep ache would set in somewhere between 1/2 mile and 3/4 mile. If I tried to push through it, I would be limping for a few days.
I went to PT until I didn't want to afford it anymore, with no change. Dr. Gross indicated that this happens in some small, but not insignificant, percentage of patients. So, I accepted it and did other things. The odd thing is that I could do an hour-long HIIT class, with squatting, box jumps, etc, with no pain. But a steady job would set it off.
Flash forward about 7 years.....I join a boot camp gym. Keep in mind that prior to resurfacing the extent of my lower-body workout was running. In boot camp, it was a constant lower-body blast. Squats, lunges, wall sits, sled pushing, box jumps, and on and on. Never had I ever worked my legs/glutes so much. Then a group of us started adding a run to the end of the class. We ran a mile and I had NO issues. So, on a weekend I went for a run. I made it 2 1/2 miles before I started noticing my hip.
So, I think that some muscle deep inside there was traumatized from the surgery enough to stop doing it's job, and the boot-camp workouts seemed to have woken it up. At least somewhat.
I know this doesn't answer the first question, but perhaps helps with some of the replies.