Hi James,
Thanks for reaching out. I will suggest you the same solution above.
Please follow the steps below,
1) Go to “Sign In Settings” tab in OAuth client plugin
2) Configure “Custom redirect URL after logout” with logout URL of OAuth Provider.
So on logout event from WordPress, we will send logout request to your OAuth provider to achieve logout from all apps.
Can you tell me plugin version you are using to confirm if this is supported with your version?
Thanks.