Many iPhone users are facing issue with iMessage freezing issue that while sending any picture using iMessage the iPhone gets stuck or freezes and you will not be able to do anything with it. The issue becomes more significant when trying to send multiple photos using iMessage as the phone hangs up while sending first picture and you will have to wait for sometimes to send another one on iMessage.
The issue is reported with new iOS11 software release and with latest iPhone X, 8 and iPhone 7,iPhone 6s as well. While selecting a photo from the photos app and clicking the box up arrow to message it via iMessage the phone hangs up and stays frozen for sometimes while sending the pictures. To make it work again you may have to click multiple times, sometimes it will respond, other times have force close Messages, and then try again. This is surely a major bug that reported from almost all iOS11 upgraded device be it an iPad mini, iPad Pro, iPhone 7 and even the latest Apple flagship iPhone X, all have this issue with iMessage.
Surprisingly the iMessage freezing issue is even reported with latest iOS11.2.5. Many users have contacted Apple for a fix and Apple has acknowledge that there is some problem that needs to be fixed.
Workaround to fix iMessage freezing in iOS11:
Workaround 1: Use Dropping the photo
Open the iMessage and drop the photos in from the message rather than selecting the photo in the photo stream and messaging from there. This may perform better to send iMessage pictures.
Workaround 2: Turn off Speak Screen
Check to see if you have Speak Screen enabled under Setting -> General->Accessibilty-> Speak screen Speech. If it is ON, disable and reboot phone.
Workaround 3: Reset Your iPhone:
Try to reboot the iphone and clean up iMessage as you may have too many messages/conversations taking up space . If those don't work try resetting all settings (Settings->General->Reset->Reset All Settings). If nothing works up, reset the phone via iTunes on your computer.