WhatsApp is probably working on two-step authentication. The function works with a six-digit code that users have to come up with and remember. How WhatsApp will use the authentication is still unknown.
The Twitter account WABetaInfo struck in the most recent beta version for Android, 2.16.183, the hidden function. The function works with a code that users have to create, change and delete themselves. Anyone who has forgotten the code can access the account via a pre-specified email address.
It is unknown how and when WhatsApp will use the feature. By default, WhatsApp sends a generated code via SMS for authentication. After that first time, WhatsApp no longer asks for authentication on the same phone. It is possible that the function is used when logging in to a new phone and restoring from a backup. To use WhatsApp Web or Desktop, this is done via a QR code that users have to scan in the app itself.
It happens more often that WhatsApp in beta versions already tests functions that only come much later in the variants that appear in the download stores. The existence of many new features comes out for the first time through the betas.