I am having the same issue with the iPhone X I just received two days ago. I try to send a photo via text—no matter how I attempt to send it, it gets stuck. I have to reboot the phone and usually that works for one photo, then it just does it again and again.
That was the first in a series of issues I had with the iPhone 7 Plus. It had so many problems I just gave up on it. That was my main complaint as I’m an artist use this feature quite often and need it working.
So far this has been inherited it looks as if, unfortunately. I absolutely love everything else about this phone. I don’t know how to use anything but Apple devices so I’m kind of stuck as I learned all this at an older age and when I have tried other devices it felt like regression.