minact-scn: useg scan erroring out with error e:12751

Lately I've met in alert.log entries the following:

minact-scn: useg scan erroring out with error e:12751

According to the Metalink it is bound with high load on the system and that an undo segment scan has failed with an ORA-12751 error.
And ORA-12751 is described as "cpu time or run time policy violation"

In my case though the load on the system is not very high and the system is actually used currently for one task only, which is a massive data pump import. The import leads to temporary lack of space for archivelogs (ORA-16038, ORA-19504, ORA-16014). Of course there is a pressure on the instance trying to save archivelogs and I suppose that this state causes such notes in alert.log.

Also emergency flushes occur then:
Active Session History (ASH) performed an emergency flush. This may mean that ASH is undersized. If emergency flushes are a recurring issue, you may consider increasing ASH size by setting the value of _ASH_SIZE to a sufficiently large value. Currently, ASH size is 8388608 bytes. Both ASH size and the total number of emergency flushes since instance startup can be monitored by running the following query:

select total_size,awr_flush_emergency_count from v$ash_info;