Downloads stack progress bar "stuck" at 100% after completion of downloads
Solution 1:
There's a bug with Google Chrome that seems to have been fixed. Make sure your Chrome is up to date.
- https://code.google.com/p/chromium/issues/detail?id=150743
Solution 2:
Duplicate of What is this line on my dock? and Can't get rid of incomplete download bar underneath dock icon
It doesn't just happen with Chrome.
FinderDock is a good solution.
Or you can just move the Downloads icon to a different place on the dock, then move it back, that usually fixes it.