We saw a materialized view snapshot error in alert log.
ORA-12012: error on auto execute of job 854
ORA-12008: error in materialized view refresh path
ORA-01401: inserted value too large for column
It could be that the definition of the master table had been changed without notice, possibly the column length.
We used to drop and recreate the materialized view in such situations before 11.2, but we can do better by modifying the column length since 11.2.
To learn how to resize column length, please refer to Oracle 12c documentation: ALTER MATERIALIZED VIEW.