BitTorrent client: trouble downloading last few blocks from peers - python-3.x

Question

The BitTorrent client I'm working on is almost working except it couldnt get the last few blocks from peers even though the requests have been sent. I get no data from peers except for keep-alive messages and peers would close their connection after sending a few keep-alive.
I know there is a end game mode, where there's a tendency for the last few blocks to trickle in slowly. But in my case, all peers would stop sending any data when there are a few blocks left and close their connection one by one.
What could be the problem that is causing this?
2016-07-19 15:05:27,131 - main.torrent_client - INFO - we have piece 69
2016-07-19 15:05:27,131 - main.torrent_client - INFO - downloaded: 71, total: 72
2016-07-19 15:05:27,132 - main.torrent_client - INFO - peer queue {70, 71}
2016-07-19 15:05:27,132 - main.torrent_client - INFO - 2 blocks left to request from 198.251.56.71
2016-07-19 15:05:27,132 - main.torrent_client - INFO - pop a block from piece 70
2016-07-19 15:05:27,132 - main.torrent_client - INFO - peer queue {71}
2016-07-19 15:05:27,132 - main.torrent_client - INFO - 1 blocks left to request from 198.251.56.71
2016-07-19 15:05:27,133 - main.torrent_client - INFO - pop a block from piece 71
2016-07-19 15:05:30,138 - main.torrent_client - INFO - requested {'index': 71, 'begin_offset': 0, 'request_length': 16384} from 198.251.56.71
2016-07-19 15:05:27,133 - main.pieces - INFO - Done requesting all the pieces!!!!!!!!!
2016-07-19 15:06:18,066 - main.torrent_client - INFO - just sent keep alive message to {'port': 57430, 'host': '198.251.56.71'}
2016-07-19 15:06:18,066 - main.torrent_client - INFO - just sent keep alive message to {'port': 29063, 'host': '38.76.93.8'}
2016-07-19 15:07:15,856 - main.torrent_client - DEBUG - Peer {'port': 29063, 'host': '38.76.93.8'} sent KEEP ALIVE message
2016-07-19 15:07:48,065 - main.torrent_client - INFO - just sent keep alive message to {'port': 57430, 'host': '198.251.56.71'}
2016-07-19 15:07:48,065 - main.torrent_client - INFO - just sent keep alive message to {'port': 29063, 'host': '38.76.93.8'}
2016-07-19 15:09:16,796 - main.torrent_client - DEBUG - Peer {'port': 29063, 'host': '38.76.93.8'} sent KEEP ALIVE message
2016-07-19 15:09:18,066 - main.torrent_client - INFO - just sent keep alive message to {'port': 57430, 'host': '198.251.56.71'}
2016-07-19 15:10:48,070 - main.torrent_client - INFO - just sent keep alive message to {'port': 29063, 'host': '38.76.93.8'}
2016-07-19 15:11:17,785 - main.torrent_client - DEBUG - Peer {'port': 29063, 'host': '38.76.93.8'} sent KEEP ALIVE message
2016-07-19 15:13:48,073 - main.torrent_client - DEBUG - connection closed by {'port': 57430, 'host': '198.251.56.71'}