I'll try to keep the backstory short: My family has an old WWII era camp that was reroofed a couple years back. At the time, money was tight so the hired help was maybe not the best.
We're currently working on renovating the camp and I've noticed that the plywood beneath the roof metal is turning black at some edges and corners. Drip edge is installed, but it appears perhaps the water is either a) running up under the edge of the metal roofing due to the low slope angle or b) causing moss on the painted fascia board which is causing water to wick up the lumber.
I'm trying to be reasonable about fixing some of these things, and am able to install some fascia myself. I'm going to kill the moss and likely install zinc strips.
What is the root cause of this problem, and how can I fix it?
I'm in West Virginia if location is very relevant.
Pic of blackened subroof from porch side