The recovery of incoming and outgoing instant messaging messages (WhatsApp, Facebook, Snapchat, Instagram, Viber) for non-rooted phones is via accessibility and access to notifications.
Incoming messages are retrieved through access to notifications. Messages not displayed in the notification bar will not be saved. Check in the settings of each application that messages received are displayed in the notification bar.
Outgoing messages are retrieved through accessibility, but the accessibility is unreliable and some messages may not be saved. Accessibility may also be disabled on its own.
The best way to recover all messages is the root method.