How do I fix my scroll bar problem?
Sometimes, when it comes to random software errors, restarting the affected program, which is the Chrome browser in your case, fixes the issue. Simply exit Chrome and then relaunch it. If this doesn't work, exit Chrome, reboot Windows and then restart Chrome.
Why do I keep losing my scroll bar?
Go to Settings / Ease of Access / Display and turn off Automatically hide scroll bars in Windows. Scroll bars will then always be full-size in many (but not all) places.