Issue Board in New Navigation: horizontal scroll bar is not visible before scrolling down

Summary

Horizontal scroll bar is not visible at the Issue Board at the page load. I have to scroll down before I see the horizontal scroll bar. (Summarize the bug encountered concisely)

Steps to reproduce

1. Turn on "New Navigation"
2. Go to "Issues" -> "Board".
3. Add multiple lists, so that a horizontal bar is needed to see all lists.
4. Refresh Page
5. You can't see the horizontal scroll bar to scroll to the right.
6. You have to scroll down with the vertical bar and then you can use the horizontal bar.

Example Project

We can use the Issue Board of the GitLab CE Project: https://gitlab.com/gitlab-org/gitlab-ce/boards

What is the current bug behavior?

The horizontal scroll bar is not visible in the issue board before scrolling down

What is the expected correct

The horizontal scroll bar should be visible on page load.

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Possible fixes

Change the height value of class ".boards-list" from height: calc(100vh - 120px); to height: calc(100vh - 180px); in the media query (min-width: 768px) in the file /app/assets/stylesheets/new_sidebar.scss on line 195.