Error when running "mayavi2"

I met a similar problem as issue #947

When I tried running "mayavi2" in terminal, I got following error:

Exception occurred in traits notification handler for object: , trait: application, old value: None, new value:
Traceback (most recent call last):
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/traits/trait_notifiers.py", line 580, in _dispatch_change_event
self.dispatch(handler, *args)
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/traits/trait_notifiers.py", line 484, in dispatch
handler(*args)
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/traits/traits_listener.py", line 412, in handle_simple
self.next.register(new)
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/traits/traits_listener.py", line 386, in register
value = getattr(self, type)(new, name, False)
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/traits/traits_listener.py", line 607, in _register_simple
return next.register(getattr(object, name))
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/envisage/ui/workbench/workbench_application.py", line 132, in _gui_default
return GUI(splash_screen=self.splash_screen)
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/mayavi/plugins/mayavi_workbench_application.py", line 121, in _splash_screen_default
show_log_messages = True,
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/pyface/base_toolkit.py", line 184, in __init__
raise NotImplementedError(msg % (toolkit, package, name))
NotImplementedError: the null pyface.ui.null backend doesn't implement splash_screen:SplashScreen
Exception occurred in traits notification handler for object: , trait: application, old value: None, new value:
Traceback (most recent call last):
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/traits/trait_notifiers.py", line 580, in _dispatch_change_event
self.dispatch(handler, *args)
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/traits/trait_notifiers.py", line 484, in dispatch
handler(*args)
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/traits/traits_listener.py", line 412, in handle_simple
self.next.register(new)
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/traits/traits_listener.py", line 386, in register
value = getattr(self, type)(new, name, False)
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/traits/traits_listener.py", line 607, in _register_simple
return next.register(getattr(object, name))
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/envisage/ui/workbench/workbench_application.py", line 132, in _gui_default
return GUI(splash_screen=self.splash_screen)
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/mayavi/plugins/mayavi_workbench_application.py", line 121, in _splash_screen_default
show_log_messages = True,
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/pyface/base_toolkit.py", line 184, in __init__
raise NotImplementedError(msg % (toolkit, package, name))
NotImplementedError: the null pyface.ui.null backend doesn't implement splash_screen:SplashScreen
Traceback (most recent call last):
File "/home/.conda/envs/cent7/5.1.0-py27/Test/bin/mayavi2", line 8, in
sys.exit(main())
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/mayavi/scripts/mayavi2.py", line 602, in main
mayavi.main(sys.argv[1:])
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/mayavi/plugins/app.py", line 195, in main
app.run()
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/mayavi/plugins/mayavi_workbench_application.py", line 73, in run
gui = self.gui
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/envisage/ui/workbench/workbench_application.py", line 132, in _gui_default
return GUI(splash_screen=self.splash_screen)
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/mayavi/plugins/mayavi_workbench_application.py", line 121, in _splash_screen_default
show_log_messages = True,
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/pyface/base_toolkit.py", line 184, in __init__
raise NotImplementedError(msg % (toolkit, package, name))
NotImplementedError: the null pyface.ui.null backend doesn't implement splash_screen:SplashScreen

When I tried running an example using mayavi library, I got following error:

Traceback (most recent call last):
File "protein.py", line 121, in
mlab.figure(1, bgcolor=(0, 0, 0))
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/mayavi/tools/figure.py", line 64, in figure
engine = get_engine()
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/mayavi/tools/engine_manager.py", line 92, in get_engine
return self.new_engine()
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/mayavi/tools/engine_manager.py", line 137, in new_engine
check_backend()
File "/home/.conda/envs/cent7/5.1.0-py27/Test/lib/python3.6/site-packages/mayavi/tools/engine_manager.py", line 40, in check_backend
raise ImportError(msg)
ImportError: Could not import backend for traitsui. Make sure you
have a suitable UI toolkit like PyQt/PySide or wxPython
installed.

I think the problem may caused by the upgrading of some dependent packages. The version of the packages are listed below:
apptools 4.5.0
certifi 2020.6.20
click 7.1.2
configobj 5.0.6
cycler 0.10.0
edempy 0.1.4
envisage 4.7.0
gitdb 4.0.5
GitPython 3.1.1
h5py 2.10.0
kiwisolver 1.2.0
matplotlib 3.3.0
mayavi 4.7.1
numpy 1.19.0
packaging 20.4
pandas 1.0.5
physt 0.4.10.1
Pillow 7.2.0
pip 20.1.1
pyface 7.0.1
Pygments 2.6.1
pyparsing 2.4.7
python-dateutil 2.8.1
pytz 2020.1
scipy 1.5.2
setuptools 49.2.0
six 1.15.0
smmap 3.0.4
traits 6.1.1
traitsui 7.0.1
vtk 8.1.2
wheel 0.34.2