CodePipeline: Could not deregister webhook with Github

I got this error while trying to delete an old pipeline on CodePipeline:

Could not deregister webhook <redacted> with GitHub. Wait a few minutes and then try again. If the problem continues, contact your AWS administrator or AWS Support. Failed on the following operation: DeregisterWebhookWithThirdParty. The following message contains details on the exception: Webhook could not be de-registered with GitHub. Error cause: Invalid credentials [StatusCode: 401, Body: {"message":"Bad credentials","documentation_url":"https://docs.github.com/rest"}]

If I try to modify the Action by switching to another repository or provider, I get this error message on save:

An unspecified error occurred. Check your network connectivity, and then check to see if there are any issues with the service at the Service Health Dashboard.

Is this a bug?