WhatsApp notification showing "Deleting all messages" My father has a Samsung Galaxy On5, Android 6.0.1-Marshmallow.

Today, all of a sudden, the WhatsApp on his phone started showing this:



I quickly restarted the phone, but the notification again came back after some time. Moreover, although it's saying it's deleting messages, no message is actually being deleted from any chat or group.

Has anyone faced something like this before? Is it some malware that's causing this? I performed a check of the phone by Malwarebytes, but everything seems to be okay.
To remove the blocking "deleting all messages" notification:


Go to Settings - Apps - WhatsApp
Press "Force stop"