Same problem. I get the notification with vibration on the gear s, but cant read the message. Just a blank screen with green circle "view content on mobile device" button and blue "clear" circle. No problem reading emails or messages on the gear s, just WhatsApp. Any fixes yet?
I used to have my S8 with Gear S2, and when I get Whatsapp messages, I can read the messages in my watch, but after One UI, I cant anymore. I switched from S8 to Note 9 and still the same issue. I do get the notifications.... but I cant read the messages in the watch, I have to unlock my phone and read them from there.