pymilvus [BUG] Stream removed

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This is a simple code i write to reproduce my bug. I use the ConnectionPool but after a while I got an error

from milvus.client.pool import ConnectionPool
from milvus import DataType, MetricType
import time

pool = ConnectionPool(uri="tcp://106.52.211.246:19530", pool_size=1)
collection_fields = [
                {"field_name": "user_id", "data_type": DataType.INT64},
                {"field_name": "embedding", "dimension": 128,
                 "extra_params": {"index_file_size": 100, "metric_type": MetricType.L2}}
            ]
conn = pool.fetch()
conn.client().create_hybrid_collection("test", collection_fields)
conn.close()

time.sleep(60*10)

conn = pool.fetch()
conn.client().drop_collection("test")
conn.close()

I run the code and got a error:

Addr [127.0.0.1:19530] drop_collection
Rpc error: <_MultiThreadedRendezvous of RPC that terminated with:
	status = StatusCode.UNKNOWN
	details = "Stream removed"
	debug_error_string = "{"created":"@1611998226.096000000","description":"Error received from peer ipv4:127.0.0.1:19530","file":"src/core/lib/surface/call.cc","file_line":1062,"grpc_message":"Stream removed","grpc_status":2}"
>
	{'API start': '2021-01-30 17:16:46.829403', 'RPC start': '2021-01-30 17:16:46.830986', 'RPC error': '2021-01-30 17:17:06.129837'}

Expected behavior A clear and concise description of what you expected to happen.

Environment details

Hardware/Software conditions(Linux)
Method of installation(Docker cpu-v0.10.5)
Milvus version(v0.3.0 & v0.4.0) I got the error in both of the two version
Milvus configuration (I just modify the cache of the server_config.yaml) Screenshots If applicable, add screenshots to help explain your problem.

Additional context Add any other context about the problem here.