Why does resetting rabbitmq qos not work

[cyoffuture]

I first set prefetch_count to 2, and then I bind the queue to a consumer, and I do get 2 pieces of data at the same time, but then I reset prefetch_count, and it doesn't work, I don't get 4 pieces of data at once.

await channel.set_qos(prefetch_count=2, global_= False)

queue = await channel.get_queue(queue_name)

consume_tag = await queue.consume(on_message)

await asyncio.sleep(3)

# reset after 3s or more time
await channel.set_qos(prefetch_count=4 , global_= False)