NOT filter operator does not on Epics Labels

Summary

When using the not equal, != filter to filter out a in a Epic list. This filter does not work. The Epics with filtered out are still shown.

The NOT operator is not working correctly for the Epic filters

This issue was reported by customer on zd-270115(internal)

Steps to reproduce

1. Create Epic. Apply labels if needed
2. Go to Epic list and filter with != operator for label, author, or other
3. Epics are not filtered

Example Project

Test project

What is the current bug behavior?

Epics are not filtered when using =! operator

What is the expected correct behavior?

Epics are filtered when using =! operator

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com