I had a similar problem last year with my girlfriend's privet hedges (I'm sure there's a joke there). They were all "sticky" and not developing really much of anything. I didn't know anything was wrong because I didn't even know what a privet was. I just thought she had dying hedges with tiny new growth leaves here and there. It wasn't until her mother mentioned their previous glory that I began looking into it.
A bit of research suggested that I could try aggressive pruning, which I did. I pruned them from about 6 feet high, down to around 18". It was kind of scary because it felt like I did something bad or wrong lol. They are supposed to be hedges, but now they're much lower than the fence line. Buuuut... This year they are back to life and flourishing with flowers and all. My girlfriend actually said she didn't know they even flowered. I guess pruning was my solution, is what I'm saying.
I'm not joking when I say that I had the exact same Pics A/B/C as you did. Pics A/B being when I noticed something was wrong, and Pic B being 1 year after pruning.
I've included 2 photos of the hedges as they look today. This is 1 year almost exactly since I pruned them.
I'm not at all sure if this will help you, but it immediately made me think of my hedges a year ago.
