Very likely you have failed forecasts somewhere in your hierarchy. The failed series need to be addressed or reconciliation will fail for all the nodes for which the failed forecasts are needed to compute the reconciled forecasts.
See also note 54702 where it says:
"It is mandatory that all series in the project have forecasts so that reconciliation succeeds for all series. If one series fails to produce statistical forecasts, then reconciliation fails for all the series whose reconciliation computation depends on the failed series."
