This sounds like the same persistent OS bug that has been around caused by the Siri suggested sharing options.
This used to happen to me. I do not have WhatsApp, however I would still have the issue. And it was intermittent.
My fix was turning off the Siri suggested sharing:
Settings>Siri & Search>Show when sharing>OFF
You may need to restart your iPad after.
Although you won’t have the convenience of the suggested sharing, you should be able to share after turning off suggested sharing.