If you enable the "Kunena - Gravatar Integration" plugin, then Kunena native avatar will be disabled. When a user went to edit his own profile on Kunena, the "avatar image" Tab will not be shown!
This is a very stupid logic!
The admin's enabling of Gravatar integration does NOT mean that he will ONLY use Gravatar avatars. The Gravatar avatar should be just an extra method, instead of an override!
The correct way is:
After enable the Gravatar integration, Kunena's native avatar still works. If some users did not upload avatar image to Kunena, then Gravatar integration will take over and check if there is a Gravatar avatar for that user. If exists, then load that Gravatar image, if no, then show empty (default) avatar image.
What if the site admin only want to show Gravatar avatar?
Very simple: just set the "allow upload avatar" option to "No" in Kunena configuration, and enable Gravatar integration plugin.
If I enabled "allow upload avatar" of Kunena, and also enabled Gravatar integration, that means: I want they BOTH work, and the Gravatar integration should work as secondary priority.