WhatsApp posted about the latest feature it is working on - logout screen, in a Wabetainfo blog post. WhatsApp is trying to fix a particular problem that might have been the reason why you are being logged off automatically. A few days ago, WhatsApp released another effective feature where users can link their Android tablets.
The screenshot gives an example where the section shows up when you are logged out from WhatsApp for some reasons:
In case, you decide to manually log out of the app from a secondary device (in this case, the tablet), go to WhatsApp Settings > Account > Log out. Or, perhaps you want to remove the existing session of your tablet from your main phone, go to WhatsApp Settings > Linked devices.
Another reason that might pull you out of your logged-in device may be unexpected and uncertain technical issues. If you have been logged out of the app, you can log into WhatsApp again by pressing the “Continue” button placed within the same section.
The logout screen is a part of a feature under development and it will be rolled out to some beta testers in a future update.