Flushing db leads to setting huge numbers of _lock keys in distributed architecture even when required key is present

[snjtkh]

We have like 30 consumers which are processing gcp pubsub data and some 4-5 web apps which are talking to redis. Everything works fine but whenever load spikes on consumers and in between if a key is expired then after setting the missed key(which is used in every consumer) it started setting _lock_key a lot which remains there until its ttl (after one expired another is set for the same key) even when required key is present. We have set expiration_time=-1 for the region.

 region = make_region(function_key_generator=kwarg_function_key_generator).configure(
    'dogpile.cache.redis',
    arguments={
                'redis_expiration_time': 60 * 60 * 8,  # 8 hours,
                'distributed_lock': True,
                'thread_local_lock': False,
                'lock_timeout': 60,
                'connection_pool': redis.BlockingConnectionPool(max_connections=50, timeout=20,
                                                queue_class=LifoQueue).from_url(os.environ['REDIS_HOST'] + '? 
                                            health_check_interval=30&retry_on_timeout=Yes&socket_timeout=20&socket_connect_timeout=10') 
                                            if gevent.monkey.is_anything_patched() else redis.BlockingConnectionPool(max_connections=50, 
                                            timeout=20).from_url(os.environ['REDIS_HOST'] + '? 
                                            health_check_interval=30&retry_on_timeout=Yes&socket_timeout=20&socket_connect_timeout=10')
                             },
    expiration_time=-1
)

@region.cache_on_arguments()
def test(data=None):
       return data

Setting bulk lock keys also spiking redis memory, isn't it some kind of thunderherd. Is it a bug or i am doing something in wrong way, please help me in understanding this behaviour.