I had this problem with rules in general when I got back into wargaming. I remember it most vividly when I got Virgin Queen, which was one of the first games I got in my initial foray back into wargaming. For some reason, the rules just did not make sense to me. It was like I was reading them in a foreign language. I thought "what's wrong with me? This shouldn't be this difficult." So I set them aside to come back to. And I had other issues with working my way through wargame rules - so it was pretty slow at first. But then I forced myself to sit down and learn 1914: Twilight in the East - it was going to be a do or die deal, and it ended up working. That helped me kind of form a system of working through the rules for complex games. Since then, I haven't had any issues with not being able to work out rules. Even went back to the Virgin Queen rules and thought "why did I find these so difficult? This doesn't seem too difficult at all!"
I had the same experience. Came back to wargaming after 20 years with Here I Stand, SPQR and Lock n' Load Heroes of the Gap. Like you said, it was like another language. I kept bouncing from rulebook to rulebook befuddled at my inability for things to click. SPQR finally cracked after treating it like a textbook and taking notes. It was frustrating at the time, but in hindsight I was able to appreciate how much rules had evolved since my Avalon Hill days.