Ever exported a whole schema containing DBMS_SCHEDULER jobs with non-default job classes?
Chances are that you hit the following error message when you attempt to import the dump later on.
ORA-39083: Object type PROCOBJ failed to create with error: ORA-27476: "SYS.MY_FANCY_JOB_CLASS" does not exist
Job classes defined with DBMS_SCHEDULER.CREATE_JOB_CLASS are not owned by the schema user but by user SYS (as inferred by looking at the error message itself).
As a result, any jobs whose job class has not been re-created before importing the dump, won't be (re)created.
If, for some reason, the script for creating the job is not readily available but you have access to the database where the dump was taken, you can quickly generate a script for the job via the "Create like" feature of SQLDeveloper.
Note however that the missing job class must be (re)created manually, SQLDeveloper doesn't help with that.
See message translations for ORA-27476 and search additional resources.