Unable to find member to add to Group despite existing

Expected behavior:

Member is discovered and available to select in the drop down menu.

Summary

When attempting to add a member to one of my Groups (specifically a Subgroup), they cannot be found in the dropdown list. However, they are infact a member. It does seem to find members who have "Z_V" in their username, however not the member "Z_V" precisely. https://gitlab.com/Z_V

Steps to reproduce

Attempt to add the member "Z_V" to a Group. They will not be found.

Example Project

N/A

What is the current bug behavior?

Z_V is unable to be found in the drop down menu when attempting to add to a Group.

What is the expected correct behavior?

Z_V shows up in the drop down menu, allowing them to be added to the Group.

(What you should see instead)

Relevant logs and/or screenshots

N/A

Output of checks

This bug happens on GitLab.com

Possible fixes

String pattern issues? Members who have Z_V as part of their username appear, but not Z_V them self.