The error occurs for the users who have signed-in using SSO (SAML).
The error message is displayed because the IdP metadata does not contain single logout service endpoints. In simple words, OpenSpecimen has no clue of where and how to reach the IdP for signing out the user session.
To fix the error, you need to contact the IdP/system administrator and get an updated IdP metadata containing a single logout service endpoint. On receiving the fixed metadata, update the SAML configuration in OpenSpecimen as described below:
Navigate to Home → Extras → Identity Providers.
Select the Domain used for SSO (type = saml)
Paste the IdP metadata in the text area provided for the same.
Without touching any other attributes/fields, click on the Update button.