I think a story is a story, and I'm not at all against screen time. I think you can work on comprehension, plot, charachter, nuance, actually by watching children's movies. You can half way pay attention as they watch something and ask questions about stuff you missed, or sit and pay full attention and start a running conversation over the movie. Point out the obvious. React to the story. Your kid will start to do the same.
If you do get a workbook with short stories and comprehension questions, the way I remember it being taught, you read the questions first, then you read the story and underline the sentences that answer the questions, then you answer the questions afterwards. They might have to re-read if they miss something. It will take some guidance from you and some practice.
Reading eggs. com has a section for ages 8 and up called reading express that teaches comprehension. There's a two week free trial and you can use two promotional codes (find them by google), so it adds up to the first month free to see if it works for your kid. You might want to sit with him and help him out, at least at first.
This is all separate from finding out why there's a problem at all to start with.
