2FA doesn't seems to be mandatory even with "Require all users in this group to setup Two-factor authentication" enabled

Summary

We have enabled the Require all users in this group to setup Two-factor authentication option at our group level, to enforce anyone joining it to have a second factor authentication enabled, but when I look at the group's member list, some have the 2FA label, some doesn't.

Steps to reproduce

1. Create a new group
2. Enable the Require all users in this group to setup Two-factor authentication option from the group's general settings
3. Join this group with a new user

What is the current bug behavior?

New users seems to be able to join without configuring a 2FA, so that they don't have the 2FA label when looking at the group's members.

What is the expected correct behavior?

The user, joining the group, should being requested to enable a 2FA and shouldn't be able to access the group's data until it is done.

Results of GitLab environment info

This happens on gitlab.com.