I faced with that issue on 11.2.0.4 version on Linux 6. There were no messages or warnings in the alert log file.

Export status showed as executing and there weren’t any errors.

I used below sql to identify wait:

select v.status, v.sid,v.serial#,io.block_changes,event
from v$sess_io io, v$session v
where io.sid = v.sid
and v.saddr in (
    select saddr
    from dba_datapump_sessions
) order by sid;

The output is like below and seems expdp hang

STATUS SID SERIAL#   BLOCK_CHANGES   EVENT
------ ---- -------  -------------  --------------------------------------------
ACTIVE 324  41        54           wait for unread message on broadcast channel

Here are some reasons to see that wait event:

1. If you have some trigger on your system such as login trigger etc. you may hit this
2. If you have this message during impdp check your alert log, possibly your tablespace need to grow up.
3. You stat have been stolen. Gather statistics on the data dictionary and system tables. You may run below command and rerun your export:

   EXEC DBMS_STATS.GATHER_DICTIONARY_STATS;
   EXEC DBMS_STATS.GATHER_SYSTEM_STATS;
   EXEC DBMS_STATS.GATHER_FIXED_OBJECTS_STATS (null);