WhatsApp is now properly optimised for Android Nougat's new notification system all thanks to a latest beta build.
This means people using the WhatsApp version 2.17.13 on their smartphones powered with Android 7.0 or 7.1 Nougat should see all messages from a conversation, both personal and group chat. So when you get a new message from the same conversation, the Quick Reply with typed text will no longer disappear.
Not only the latest message, it will also correct notification unbundling behaviour of conversations and expansion of multiple messages. In addition to that the latest WhatsApp update fixes notifications on Android Wear devices, making them more readable and reply quickly without any issue.
With the latest beta you will no longer have to deal with the notification system wherein only the most recent message shows up, not the whole notification, according to a report by AndroidPolice.
To test the WhatsApp notification you will need to be on the version 2.17.13, which is now available to download in form of APK mirror.
Alternatively, enrol into the testing program for WhatsApp messenger through Play Store that lets users experience the updates including beta version of the app. You might also consider waiting until the public version is rolled out in the Google Play Store.