"My guess is the middle third of the left limb is too stiff."
This is almost certainly correct, but a lot more is going on you need to address. It does need more "floor-tillering".
Definitely get on those fades. They are called "fadeouts"for a reason. Next, DON'T pull it to 85 lbs again.
If you aren't confident with floor tillering, you know from the picture where it is too stiff, right? Grab a crayon and mark all those areas. Color em up good! DO NOT mark where it is bending already. Then get your rasp and rasp off all the marks. Finally, scrape off all the rasp marks.
Do this maybe TWICE on the whole stiff limb, then check the bow on the tree again and DO NOT pull it past what you intend it to pull. If you want 50 lbs, pull it with 50 lbs ONLY. After the first time, do only one pass before checking.
Good luck. Hit Jawge's site, you won't be sorry.