Summary

The vertical scrollbar and its slider are being hidden by backlog and/or sprint header in JIRA Software 7.4.x

Environment

• JIRA Software 7.4.x

• Steps to Reproduce

1. Create a test Scrum or Kanban board with sample data
2. Go the backlog for this board
3. If the board has a lot of issues, then the scrollbar won't actually be visible at all to the users
4. You can resize the browser window in order to see this better and to play with this, but JIRA shouldn't be obscuring this from the page view

Expected Results

JIRA Software should be displaying the entire scrollbar when applicable. You should be able to see the entire scroll piece to know what part of the page you are on at any given time.

Actual Results

The scrollbar, and its slider, can be completely or partially obscured by the backlog header on the page. (see screenshot)

Notes

• This is not reproducible in JIRA 7.3.6 or earlier versions in my testing.
• I was able to repro this with JIRA 7.4.0 and in 7.4.2 in both latest Firefox 54.0.1 and latest Chrome 59.0.3071.115 versions
• Customer also reported this problem in 7.4.1
• Reportedly IE does display this correctly.

Workaround

• Focus the backlog (by clicking anything inside it, like the sprint header or issues) and scroll using mouse weel/touchpad/arrow keys
• Click on the sidebar below the header, this will bring the scrollbar to clicked position making it visible

Update: 
You can toggle the sticky header feature on and off for the instance at 
Settings > Applications > Jira software Configuration> Sticky sprint headers
The feature will be on by default. You can turn the  feature off to get the behavior prior to 7.4 releases, which will keep the scrollbar visible. 

Turning off "Sticky sprint headers" will prevent users who are using Firefox from being able to find entries in the backlog by using "CTRL + F" shortcut.