After investigations, commit the proposed patch by kklimonda presented with the following introduction : cm/templates/site/login_form.html template uses a relative url for the form action, which seems to break deployment in the subfolder when trailing slash is missing (the form redirects to the upper folder breaking login). Using {% url login %} (as in the attached patch) instead would fix the issue.

from cm.tests.test_notifications import *
#from cm.tests.test_converters import *
from cm.tests.test_spannifier import *
from cm.tests.test_comment_positioning import *
from cm.tests.test_structure import *
from cm.tests.test_history import *
from cm.tests.test_security import *
from cm.tests.test_activity import *
from cm.tests.test_registration import *
from cm.tests.test_api import *