3394582 - Identity Provisioning fails with error "User or Password configured for the provisioning system are empty or not specified at all"

Identity Provisioning (IPS) job where Identity Authentication (IAS) is a system finished with error:

org.quartz.JobExecutionException: Cannot execute provisioning job in tenant context: <IAS tenant ID>
Caused by: com.sap.cloud.ips.connector.exception.ProvisioningRuntimeException: Error during execution on behalf of tenant with ID: <IAS tenant ID>
Caused by: com.sap.cloud.ips.runtime.exception.ProvisioningException: Executing delta load failed. 
Caused by: com.sap.cloud.ips.connectors.api.ConnectorException: Connector cannot process more entities due to irreparable error 
Caused by: com.sap.cloud.ips.connector.exception.ProvisioningRuntimeException: User or Password configured for the provisioning system are empty or not specified at all.

OR

org.quartz.JobExecutionException: Cannot execute provisioning job in tenant context: <IAS tenant ID>
Caused by: com.sap.cloud.ips.connector.exception.ProvisioningRuntimeException: Error during execution on behalf of tenant with ID: <IAS tenant ID>
Caused by: com.sap.cloud.ips.runtime.exception.ProvisioningException: Executing delta load failed. 
Caused by: com.sap.cloud.ips.connectors.api.ConnectorException: Connector cannot process more entities due to irreparable error 
Caused by: com.sap.cloud.ips.connectors.api.CallbackFatalException: All <source, target or proxy> systems are marked as invalid due to the following reasons: [<IPS System ID> - User or Password configured for the provisioning system are empty or not specified at all.]

• Identity Provisioning
• SAP Cloud Identity Services

source, target, proxy, credentials, authentication, authorization, 401 , KBA , BC-IAM-IPS , Identity Provisioning Service (IPS) , BC-IAM-IDS , Identity Authentication Service , Problem