17 and 18 are not swapped because 'Gin' says 'give me a heads up' after Momo took a picture because he was caught off guard — he says that so Momo should have actually warned him beforehand. And you're confusing the profile picture thing. Momo asks him if he can have it as a profile picture, not if he's allowed to take a photo.
Oh, I see. I was really confused. I'm sorry for my mistake.
In my perception at the time, the flow seemed disrupted when I read it, like thoughts were interrupted by random moments.
I did think that he took a photo then asked permission for the profile picture, but with the way I read it, it looked like:
"Mind if I use this as profile picture"
My thoughts: "What does he mean "this" as a profile picture? Did he take any pictures earlier and I just didn't see it?"
--> "No, but if you do that, then all your friends would think we're close" --> Takes photo.
My thoughts: "Hm, that's strange. Why would they talk about a photo that has yet to exist and then the picture is taken in the next page? Maybe it's mixed up!"
So it was like he asked for permission to make it a profile picture, without taking the picture yet, and Gin allowed it but was still caught off guard when the actual picture was taken,
Plus the way the memories of their past was depicted and talked about after Momo said, "In the end", so it felt like it was cut off, then brought back all of a sudden.
But I do understand that I could be wrong, so I'm very sorry. And I was so confident about that part, how embarrassing...

Ch. 2:
Pg. 17 and 18 are mixed up, pg. 23 and 24 are mixed up.
Pg. 17-18
I was able to find out because it seemed strange that "Give me a head's up" and "Profile picture" were mentioned before the actual picture taking. Also, Momo mentions the memories of them talking about dyeing their hair, but the page that came first was one that begun with "In the end, we never really got the chance to show each other..." before the actual memories.
Pg. 23 and 24
This I didn't spot right away, but thanks to pg. 22 and 25 I was able to rearrange it in my mind. It just seemed odd that he'd look around first then think of sad thoughts, then spot the stuffed toy, when it makes more sense if the sad thoughts continued on from pg. 22 like this:
"It's the same for me"
--> " It hurt seeing him with other people - because I wanted to be with Momo too"
--> Looks around
--> Spots toy
I could be wrong, but I'm at least confident about pg. 16-17. If this gets corrected, please disregard my comment.