I have this happen, I noticed reading is something I kind of need to practice. Maybe short comments ruined my brain lol.

I started getting into reading long books again last year. The beginning was rough, I was starting to think there was something wrong me. Sometimes I still do, but just being consistent and not hard on my self, I'm able to focus longer on reading and enjoy it. Some books and authors are easier then others too. LOTR series was work at times, enders game was pretty easy.

Alot if non fiction sucks too though and is pretty long winded.

If your worried about missing out on writing, there are short stories, and novellas to read