Epics dropdown returns "No matching result" in sidebar

Summary

After assigning or changing an epic using the dropdown in the sidebar, immediately clicking on the dropdown shows "No matching result".

The issue is present wherever ee/app/assets/javascripts/vue_shared/components/sidebar/epics_select/base.vue is used.

E.g.,

• issue show sidebar
• group/project boards sidebar
• epic swimlanes (group and boards) sidebar

The epic select dropdown works correctly after a page refresh.

Example Project

Visit https://gitlab.com/gitlab-org/plan-stage/test-project/-/issues/2

Try assigning this epic to the issue using the sidebar's epic select dropdown: &5172

Then immediately click "edit" again after the assignment operation.

Relevant logs and/or screenshots

issue sidebar	epic swimlanes
Screen_Recording_2021-03-16_at_9.44.42_AM	Screen_Recording_2021-03-16_at_9.45.35_AM