I have seen FUE donor areas take as long as 6 months to recover, but not 8 months as yet.
The problem with FUE is that it causes a lot of damage to the surrounding vasculature, especially megasession FUE transplants. This is because all those little incisions add up to a big incision. The small incisions coalesce together to form a fibrotic sheet that is hostile to vascular regrowth. Add to this the fact that a large number hairs were removed from the area and you have thin patches like yours.
Over harvesting in FUE hair surgery might be possible but 8 months is a bit more than usual recovery after such problems.It is better to check with your hair surgeon soon as possible.
Thinning of the donor area is one of the factors that has to be discussed as a potential side effect of FUE harvesting with the client. When the surgeon harvests from the back and moves the hair to the front, the areas where the hair was taken from will not grow hair and leaves a small scar for each punch. This will result in general thinning in the donor area. This becomes more apparent in larger sessions of FUE.
The only reason I know of for loss of donor area 8 months post op from FUE would be over harvesting. You should first go back to the original surgeon and get his/her opinion of the situation.
If the area is to thin from over harvesting, then cellular therapy might be a good option to help stimulate any remaining stem cells in the area to grow.
They are moved. The art is in harvesting just the right amount. If its thin it may be shock or over harvest. This harvesting may look thin if they over harvest a small area (many non-western countries do large cases to please the patient not warning of the over harvest).
First, go back to your doctor to get his/her opinion. There are man causes for this and without examining you, I can not tell over the internet what is going on.
There are two reasons for the sparse density. First could be shock loss, for which you need a dermatologist to help to stimulate those hairs intro anagen (growth phase). Second could be over harvesting from that area. If too much hair was harvested from that area, it will stay sparse and the only treatment would be transplanting grafts into that area.
Your donor hair will NOT grow back after harvesting of grafts. If too much FUE grafts were taken your donor area will look "thin". If you are concerned see your doctor for a recheck.