ORA-16854: apply lag could not be determined in DGMGRL

On one of our Data Guard Architecure appeared below error in DGMGRL, when checked the configuration status but the primary and standby databases are fine with no delay and in syncronize.

ORA-16854: apply lag could not be determined

DGMGRL> show database verbose testdbst;

Database - testdbst

  Role:               PHYSICAL STANDBY
  Intended State:     APPLY-ON
  Transport Lag:      0 seconds (computed 1 second ago)
  Apply Lag:          (unknown)
  Average Apply Rate: (unknown)
  Active Apply Rate:  (unknown)
  Maximum Apply Rate: (unknown)
  Real Time Query:    ON
  Instance(s):
    testdbst

  Properties:
    DGConnectIdentifier             = 'testdbstby'
    ObserverConnectIdentifier       = ''
    LogXptMode                      = 'ASYNC'
    RedoRoutes                      = ''
    DelayMins                       = '0'
    Binding                         = 'OPTIONAL'
    MaxFailure                      = '0'
    MaxConnections                  = '1'
    ReopenSecs                      = '300'
    NetTimeout                      = '30'
    RedoCompression                 = 'DISABLE'
    LogShipping                     = 'ON'
    PreferredApplyInstance          = ''
    ApplyInstanceTimeout            = '0'
    ApplyLagThreshold               = '30'
    TransportLagThreshold           = '30'
    TransportDisconnectedThreshold  = '30'
    ApplyParallel                   = 'AUTO'
    ApplyInstances                  = '0'
    StandbyFileManagement           = 'AUTO'
    ArchiveLagTarget                = '900'
    LogArchiveMaxProcesses          = '4'
    LogArchiveMinSucceedDest        = '1'
    DataGuardSyncLatency            = '0'
    DbFileNameConvert               = '+DATA1/testdb, +DATA2/testdbst, +RECO1/testdb, +REC2/testdbst'
    LogFileNameConvert              = '+DATA1/testdb, +DATA2/testdbst, +RECO1/testdb, +RECO2/testdbst'
    FastStartFailoverTarget         = ''
    InconsistentProperties          = '(monitor)'
    InconsistentLogXptProps         = '(monitor)'
    SendQEntries                    = '(monitor)'
    LogXptStatus                    = '(monitor)'
    RecvQEntries                    = '(monitor)'
    PreferredObserverHosts          = ''
    StaticConnectIdentifier         = '(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=testdbst-dg-vip)(PORT=1522))(CONNECT_DATA=(SERVICE_NAME=testdbst)(SERVER=DEDICATED)))'
    StandbyArchiveLocation          = 'USE_DB_RECOVERY_FILE_DEST'
    AlternateLocation               = ''
    LogArchiveTrace                 = '0'
    LogArchiveFormat                = '%t_%s_%r.dbf'
    TopWaitEvents                   = '(monitor)'

  Log file locations:
    Alert log               : /u01/app/oracle/diag/rdbms/testdbst/testdbst/trace/alert_testdbst.log
    Data Guard Broker log   : /u01/app/oracle/diag/rdbms/testdbst/testdbst/trace/drctestdbst.log

Database Status:
SUCCESS

Solution: 

1) Connect to the standby database and check if MRP process is still running If MRP process is still running, cancell it with command:

ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;

and start MRP process with command:

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE DISCONNECT FROM SESSION;

2) if above Solution will not work try to just restart standby database. 

3) If there is still prolem with warning "about apply lag could not be determined" you can disable lag computation with next command in DGMGRL

DGMGRL> edit database 'testdbst' set property 'ApplyLagThreshold'=0;

This definitely will solve your problem.