Even python3 environment is activated, JupyterLab cannot be launched properly

When I activate my ipykernel_py3 environment and try to launch Jupyter Lab in terminal, I get the repeated error messages as follows:

Macintosh-8:~ yuenfannie$ source activate ipykernel_py3
(ipykernel_py3) Macintosh-8:~ yuenfannie$ jupyter lab
[I 12:38:19.969 LabApp] JupyterLab alpha preview extension loaded from /Users/yuenfannie/anaconda2/lib/python2.7/site-packages/jupyterlab
JupyterLab v0.27.0
Known labextensions:
[I 12:38:19.971 LabApp] Running the core application with no additional extensions or settings
[I 12:38:19.979 LabApp] Serving notebooks from local directory: /Users/yuenfannie
[I 12:38:19.980 LabApp] 0 active kernels 
[I 12:38:19.980 LabApp] The Jupyter Notebook is running at: http://localhost:8888/?token=81a366305f2a328dfbbc9cfcf757a30e4977d3abab54cb0f
[I 12:38:19.980 LabApp] Use Control-C to stop this server and shut down all kernels (twice to skip confirmation).
[C 12:38:19.981 LabApp] 

    Copy/paste this URL into your browser when you connect for the first time,
    to login with a token:
        http://localhost:8888/?token=81a366305f2a328dfbbc9cfcf757a30e4977d3abab54cb0f
[I 12:38:20.229 LabApp] Accepting one-time-token-authenticated connection from ::1
[I 12:38:22.881 LabApp] Kernel started: cf6886dd-5475-4e1e-972c-8e4614451f0e
[I 12:38:24.074 LabApp] Adapting to protocol v5.0 for kernel cf6886dd-5475-4e1e-972c-8e4614451f0e
[E 12:38:24.078 LabApp] Uncaught exception GET /api/kernels/cf6886dd-5475-4e1e-972c-8e4614451f0e/channels?session_id=5c81adbda104d35cec3acd907d6decc4&token=81a366305f2a328dfbbc9cfcf757a30e4977d3abab54cb0f (::1)
    HTTPServerRequest(protocol='http', host='localhost:8888', method='GET', uri='/api/kernels/cf6886dd-5475-4e1e-972c-8e4614451f0e/channels?session_id=5c81adbda104d35cec3acd907d6decc4&token=81a366305f2a328dfbbc9cfcf757a30e4977d3abab54cb0f', version='HTTP/1.1', remote_ip='::1')
    Traceback (most recent call last):
      File "/Users/yuenfannie/anaconda2/lib/python2.7/site-packages/tornado/websocket.py", line 546, in _run_callback
        result = callback(*args, **kwargs)
      File "/Users/yuenfannie/anaconda2/lib/python2.7/site-packages/notebook/services/kernels/handlers.py", line 262, in open
        super(ZMQChannelsHandler, self).open()
      File "/Users/yuenfannie/anaconda2/lib/python2.7/site-packages/notebook/base/zmqhandlers.py", line 176, in open
        self.send_ping, self.ping_interval, io_loop=loop,
    TypeError: __init__() got an unexpected keyword argument 'io_loop'

The opened JupyterLab Alpha Preview does not work at all. Unfortunately I have no clues why this happens. Any suggestions are welcome!