There are limits to how many photos you can share in at once from the Photos app. Probably to keep you from starting something that will take forever to finish, or overload the recieving app, or maybe the system buffers. No idea, really, what the actual reasons for each choice were. I just hope/trust that there was some reason for the choices.
For instance, you can only share 5 photos at a time using Mail. Apparently you can only share 10 at a time to FaceBook, and most other apps.
Depending on what app you are using/sharing to, you may be able to bypass this limitation in that app; if the developer gave you direct access to photos from that app.
For instance, you can select more than 10 photos to share in the FaceBook app. How well it will work when you actually do the post, I don't know. I've never had 10 photos I wanted to post to FaceBook at once. At least not from my iPad.
Good luck.