"Reply to comment" button does not work for resolved threads on merge request diff

Steps to reproduce

• comment on merge request diff
• add reply
• resolve thread
• refresh page
• click "reply to comment" button

Example Project

https://gitlab.com/gitlab-org/gitlab-ee

What is the current bug behavior?

Nothing happens and no error is shown:

Screen_Recording_2019-09-12_at_15.21.55

What is the expected correct behavior?

Reply field is shown.