dg端drop standby log报错ORA-00261 ORA-00312

系统：centos 7.9 64位
数据库：oracle 11.2.0.4 64位
环境：rac(双节点) + dg
问题描述：dg端drop standby log报错ORA-00261、ORA-00312，如下所示：
SQL> select a.thread#,a.group#,b.member,b.type,a.bytes/1024/1024 MB from v$standby_log a,v$logfile b where a.group#=b.group#;

   THREAD#     GROUP# MEMBER                                                       TYPE            MB
---------- ---------- ------------------------------------------------------------ ------- ----------
         1         10 /u01/app/oracle/oradatastandby10.log                         STANDBY         50
         1         10 /u01/app/oracle/oradatastandby10b.log                        STANDBY         50
         1         11 /u01/app/oracle/oradatastandby11.log                         STANDBY         50
         1         11 /u01/app/oracle/oradatastandby11b.log                        STANDBY         50
         1         12 /u01/app/oracle/oradatastandby12.log                         STANDBY         50
         1         12 /u01/app/oracle/oradatastandby12b.log                        STANDBY         50
         2         13 /u01/app/oracle/oradatastandby13.log                         STANDBY         50
         2         13 /u01/app/oracle/oradatastandby13b.log                        STANDBY         50
         2         14 /u01/app/oracle/oradatastandby14.log                         STANDBY         50
         2         14 /u01/app/oracle/oradatastandby14b.log                        STANDBY         50
         2         15 /u01/app/oracle/oradatastandby15.log                         STANDBY         50
         2         15 /u01/app/oracle/oradatastandby15b.log                        STANDBY         50

20 rows selected.
SQL> alter database drop logfile group 10;
alter database drop logfile group 10
*
ERROR at line 1:
ORA-00261: log 10 of thread 1 is being archived or modified
ORA-00312: online log 10 thread 1: '/u01/app/oracle/oradatastandby10.log'
ORA-00312: online log 10 thread 1: '/u01/app/oracle/oradatastandby10b.log'
异常原因：RFS进程未释放当前standby redo log文件.
解决过程：
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 1586708480 bytes
Fixed Size                  2253624 bytes
Variable Size             989859016 bytes
Database Buffers          587202560 bytes
Redo Buffers                7393280 bytes
Database mounted.
Database opened.
SQL> select open_mode from v$database;

OPEN_MODE
--------------------
READ ONLY

SQL> select process,status from v$managed_standby;

PROCESS   STATUS
--------- ------------
ARCH      CONNECTED
ARCH      CONNECTED
ARCH      CONNECTED
ARCH      CONNECTED
SQL> alter database drop logfile group 10;

Database altered.