An update for my environment:
* I installed e-commerce manually and set it up to run with gunicorn, nginx the same way the Open edX configuration does.
* E-commerce runs with ecommerce user and her own python environment.
[Tue Jun 26 16:37:06.692002 2018] [:error] [pid 63670] Traceback (most recent call last):
[Tue Jun 26 16:37:06.692004 2018] [:error] [pid 63670] File "/path/apps/edx/venvs/edxapp/lib/py$
hon2.7/site-packages/django/core/handlers/base.py", line 119, in get_response
[Tue Jun 26 16:37:06.692007 2018] [:error] [pid 63670] resolver_match = resolver.resolve(request.path_info$
[Tue Jun 26 16:37:06.692010 2018] [:error] [pid 63670] File "/path/apps/edx/venvs/edxapp/lib/py$
hon2.7/site-packages/django/core/urlresolvers.py", line 387, in resolve
[Tue Jun 26 16:37:06.692012 2018] [:error] [pid 63670] raise Resolver404({'tried': tried, 'path': new_path$
)
[Tue Jun 26 16:37:06.692081 2018] [:error] [pid 63670] Resolver404: {u'path': u'basket/single-item/', u'tried'$
[[<RegexURLPattern root ^$>],...
According to the logs, LMS cannot resolve /basket/single-item/ url for some reason.