I've just updated my watch series 6 to IOS11 and since doing that my watch no longer makes the classic notification “ding” when I receive a Whatsapp message.
How to receive WhatsApp notifications on your Apple Watch · Go to Settings. · Tap on WhatsApp. · Enable Alerts on the Lock Screen. · Go to the Watch ...
Go to Settings > Notifications > WhatsApp > turn on Allow Notifications. Next, open the Watch app, select Notifications, and turn on WhatsApp.
The fix was to go to the WhatsApp notifications settings on the iPhone and turn off Siri Announce. Hopefully this helps anyone else looking for a solution.
To set up WhatsApp notifications on your Apple Watch, start by opening the Settings app on your iPhone. Navigate to Notifications, then select WhatsApp.