edX seems to return user_id of deleted/existing users

Hello. I am a developer of the widget that can be integrated into LMS and the the chosen environment is edX that is driven on latest tutor distribution.
One of the functionalities of this widget is creation of GitLab repository with random credentials that are bound with user_id that edX returns (32 digit hex value). This widget was tested by QA and during this test hundreds of new users were automatically created. After all the tests those users were deleted via CMS logging in as staff and manual deleting via “/admin/auth” path. They seem to be deleted completely, right?
After one week we’ve noticed that newly manually registered users (via LMS “Sign Up” page) receive old repositories and it means that open edX returns the user_id of deleted/existing users. The chronological sequence persists (meaning that every user being registered last receives “newer” repository credentials). I can’t tell whether this id belongs to a deleted user or not yet. Are there any ideas about it? Maybe we do something wrong? Our widget is running on Java so we don’t have enough competence to inspect edX source code completely.