Insufficient Privileges when logged in as another user also impact Open ID connect

If you’re using Salesforce as a SAML identity provider for single sign-on (SSO) and you try to log in to your service provider. In this scenario, you’re blocked from logging in as another user and you receive an Insufficient Privileges error. 
Additionally, even when using an OpenID Connect SSO configuration, "login as" fails with the same error.

Insufficient Privileges Error:
You do not have the level of access necessary to perform the operation you requested. Please contact the owner of the record or your administrator if access is necessary.