django test runner do not see tests on py2 version, but see them on py3

When I run a command on py3:

python manage.py test myproject.user_management --settings mysettings.py

I see all my tests working fine:

Ran 29 tests

But the same command on py2:

Ran 0 tests

Command on py2 is only working when I add tests folder to command, like:

python manage.py test myproject.user_management.test --settings mysettings.py

I already: 1. Double check my imports an __init__.py in all folders and sub folders 2. Settings etc.

My app structure looks like:

project_name
----user_management
--------__init__.py
--------tests
------------__init__.py
------------training
----------------__init__.py
----------------training.py

In python manage.py shell I can easy do:

from axis.user_management.tests import TrainingViewSetTest

This behaviour happens only for few apps in my project.