Attaching a file to a tag from UI doesnt work

Summary

"Attach a file" to repository tag doesn't work. GitLab Enterprise Edition 11.7.0-ee on premises

Steps to reproduce

1)Create tag. 2) Go to /tags/ 3) Click on "Edit release notes" for any tag 4) On page /tags//release/edit try to click on "Attach a file" in lower right corner 5) Nothing happens expected: popup prompting to select a file for upload

What is the current bug behavior?

popup doesnt open and nothing happens

What is the expected correct behavior?

popup prompting to select a file for upload