Here is the log when the issue happens. The producer continues to reconnect to the broker, but the fenced state of the topic is always true.
```
19:01:42.351 [pulsar-io-4-1] INFO  org.apache.pulsar.broker.service.ServerCnx - [/10.24.34.151:48052][persistent://public/default/test-8] Creating producer. producerId=8
19:01:42.352 [Thread-174681] INFO  org.apache.pulsar.broker.service.ServerCnx - [/10.24.34.151:48052] persistent://public/default/test-8 configured with schema false
19:01:42.352 [Thread-174681] WARN  org.apache.pulsar.broker.service.AbstractTopic - [persistent://public/default/test-8] Attempting to add producer to a fenced topic
19:01:42.352 [Thread-174681] ERROR org.apache.pulsar.broker.service.ServerCnx - [/10.24.34.151:48052] Failed to add producer to topic persistent://public/default/test-8: producerId=8, org.apache.pulsar.broker.service.BrokerServiceException$TopicFencedException: Topic is temporarily unavailable
```

After check the heap dump of the broker, the `pendingWriteOps` is 5, this is the reason why the topic can not recover from the fenced state.

The topic will change to unfenced only the `pendingWriteOps` is 0, details can find at [PersistentTopic.decrementPendingWriteOpsAndCheck()](https://github.com/apache/pulsar/blob/794aa20d9f2a4e668cc36465362d22e042e6e536/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/persistent/PersistentTopic.java#L463)

But after checking the ML state of the topic, it shows the `pendingAddEntries` is 0 which not equals to `pendingWriteOps` of the topic.
The root cause is we are polling add entry op from the `pendingAddEntries` in multiple threads, one is the the ZK callback thread when complete the ledger creating (https://github.com/apache/pulsar/blob/794aa20d9f2a4e668cc36465362d22e042e6e536/managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerImpl.java#L1406, https://github.com/apache/pulsar/blob/794aa20d9f2a4e668cc36465362d22e042e6e536/managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerImpl.java#L1669),
another one is the ML worker thread when complete the add entry op (https://github.com/apache/pulsar/blob/794aa20d9f2a4e668cc36465362d22e042e6e536/managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/OpAddEntry.java#L181)

After the ongoing add entry op complete, but the corresponding op might been polled by the `clearPendingAddEntries` method. So it will poll another one, but due to
not equals to the current op, the polled op will not get a chance to be failed, so that the `pendingWriteOps` will not change to 0.

I have attached the complete logs for the topic:

The fix is to complete the add entry op with ManagedLedgerException if the polled op is not equals to the current op.