codis3添加sentinel之后点击“SYNC”异常

codis3中添加完sentinel，状态还是（OUT OF SYNC），手动点击SYNC之后报错：
```
{
"Cause": "context deadline exceeded",
"Stack": [
{
"Name": "github.com/CodisLabs/codis/pkg/utils/redis.(*Sentinel).dispatch",
"File": "/usr/local/gopkg/src/github.com/CodisLabs/codis/pkg/utils/redis/sentinel.go",
"Line": 103
},
{
"Name": "github.com/CodisLabs/codis/pkg/utils/redis.(*Sentinel).monitorGroupsDispatch",
"File": "/usr/local/gopkg/src/github.com/CodisLabs/codis/pkg/utils/redis/sentinel.go",
"Line": 448
},
{
"Name": "github.com/CodisLabs/codis/pkg/utils/redis.(*Sentinel).MonitorGroups.func2",
"File": "/usr/local/gopkg/src/github.com/CodisLabs/codis/pkg/utils/redis/sentinel.go",
"Line": 505
}
]
}
```
请问是什么原因？