"Add reaction" on merge request comment hangs for several seconds

Summary

If I click to the "Add reaction" icon on a merge request comment it hangs for several seconds before displaying the emoji panel. This bug probably starts with GitLab 13.5 (and older version didn't contain it).

Steps to reproduce

1. Create a merge request.
2. Add a comment to it.
3. Click to "Add reaction" (the "smile" icon) on the comment.

Example Project

https://gitlab.com/lukasjelinek/example

What is the current bug behavior?

It hangs for several seconds (cca 10) before it displays the emoji selection panel.

What is the expected correct behavior?

The emoji selection panel is displayed immediately without hanging.

Relevant logs and/or screenshots

None relevant.

Output of checks

None relevant.

Results of GitLab environment info

None relevant.

Results of GitLab application Check

None relevant.

Possible fixes

None relevant.