When attempting to load a specific Cost Plan, in the 'Financials' tab of the Modern UX, an error is thrown. Its corresponding message in the app-ca.log is as below.
ERROR ... services.costPlanDetailInsertService ... Exception while inserting cost plan detail
com.niku.union.persistence.PersistenceApplicationException: java.sql.SQLIntegrityConstraintViolationException: ORA-00001: unique constratint (FIN_COST_PLAN_DETAILS_U1) violated.
This same Cost Plan opens without an issue in the Classic UI.
When rows are added to a Cost Plan, values against each Grouping Attribute is mandatory. Actual Cost reported against the parent Project of the Cost Plan, had a value missing against one of the Grouping Attributes.