ORA-00600: internal error code, arguments: [krfg_mgen_coord2], [], [], [], [], [], [], [], [], [], [], []

Description
    A standby media recovery session may suddenly fail with
    ORA-600 [krfg_mgen_coord2]
   
Look for all the following:
    - this is a RAC standby, with more than one running standby
      instance
    - on the RAC standby instance performing media recovery, the
      recovery session terminates with ORA-600 [krfg_mgen_coord2]
    - flashback is enabled for the standby database
        ie "select flashback_on from v$database" returns 'YES'.
    - in the alert log of one of the other running standby instances
      check the messages written for the most recent database mount
      operation, the mount will have completed, but:
        - the message "Successful mount of redo thread <n>" will
          be there, but the following query on the standby:
             select rtnum "thread#",
             decode(bitand(rtsta,128), 128, 'FB_ENABLED_FOR_THREAD',
                    'FB_DISABLED_FOR_THREAD') "FLASHBACK"
               from x$kccrt;
          returns either no row for thread# <n>, or else it returns
          one row for thread# <n> row showing flashback is disabled
          for that thread.

Workaround
    To prevent the problem, any threads mounted on the standby
    instance need to already have flashback enabled for the thread.
    To check this, run these 2 queries on the standby:
        select thread# from gv$instance;
        select rtnum "thread#",
         decode(bitand(rtsta,128), 128, 'THREAD_ENABLED_FOR_FLASHBACK',
               'THREAD_DISABLED_FOR_FLASHBACK') "THREAD_FLASHBACK_STATE"
           from x$kccrt;