I faced a similar thing at one point. The thing that fixed it for me was going back to fiction. Started with a fantasy series. Did a little sci-fi. Did some easy classics (e.g. Dracula). Eventually that joy of reading, long focused reading, and effortless comprehension all came back. Just took practice.

Much like advice for writer's block being often "just write!". The same goes for reading. Start with something easy breezy and eventually it'll all start flowing again IMO.