FACEBOOK COMMON!
I get that they released the app because they had a deal with windows 10, but after so much time can't you at least improve it a tiny bit? Even with a webapp from messenger it works faster.
-I got a text
-Open the app
-LOADING
-LOADING| Got tired unlocked phone
-LOADING| turn on wifi
-LOADING| open the conversation
-LOADING CONVERSATION| replied
-FINALLY FINISHED AND I NO LONGER NEED IT

Now how to fix this? First try not to have a IOS imported app, try to add quick reply in the notification. YEP thats a thing! Skype UWP at least has that going for them.