I recently wondered something similar. I "learned" to play music as a child, but could never follow the notes so used to memorize the tune and use the staves as a reference for the timings. Other than with music, my reading has always been above average.

I've always assumed this was laziness on my part, and so I've recently tried to re-learn music reading, and it is getting easier (recently found PianoBooster software which has been quite useful), but still finding it difficult to read even a single note.

There was a recommendation when I went to Uni to get tested for dyslexia, even if you have no symptoms, because more people have it than you would think. And given that there is a range of types and symptoms, the possibility that this is a form of dyslexia is reasonably high.

That said, the fact that anyone can read anything is fairly remarkable when you think about it. I don't know whether we have any evolutionary basis for the repeated recognition of small characters, but I doubt it, and if so the fact that a large proportion of our brains are malleable enough to be trained for it is something impressive.

I'm just gonna have to keep practising and hope something clicks. Good luck!

This seems pretty normal. I suspect this is similar to reasons why it's hard to read a really wide line of text, or that some people put a sheet of paper under their current line while reading. Something about how our minds can manage smaller groups more easily. Probably related to how telephone numbers split up and why we put commas or spaces in numbers like 1,000,000.

Counting zeros is challenging enough that commas are added to help, so I’d say it’s normal.

For most disorders, a mild case is "normal". People who have more severe cases are classified as "abnormal". (And people who have less severe cases than normal are classified gifted/talented/superpowered.)