Group Milestone - Description markdown editor buttons and preview not working

We are using gitlab.com to host one of our projects.

When we try to create a milestone under our group space we cannot use markdown editor buttons and preview just shows a "Loading..." message indefinitely.

Steps to reproduce

• Login gitlab.com and navigate to your group.
• Click Milestones and then New Milestone.
• Type in the name of the milestone.
• Focus description field
• Click any markdown editor button -> Nothing happens.
• Type testing markdown editor, select word "markdown" and click any markdown editor button -> Selection is lost and nothing happened.
• Clear description field and type Just *testing* in the description field and Click Preview -> Nothing happens, just the "Loading..." message.

Platform Details

• Operating System: macOS 10.12.2
• Browser 1: Google Chrome 55.0.2883.95 (64-bit)
• Browser 2: Safari 10.0.2 (12602.3.12.0.1)
• Browser 3: Firefox 48.0.2