You can change this in the System Preferences to always show the scroll bar. If you click on the System Preferences icon on your dock (looks like a gear) then click on General or click the apple in the upper left and click on the General Tab, you will see the screen below.
Under "Show scroll bars:" click in the circle in front of "Always". Then you can class the preferences window. The issue of missing scroll bars should be resolved.
Want to learn more about your Mac? Then log into SU's Atomic Learning site here with your SUNet Username/password. You can also request to be added to SU's Training Development Coordinators Tips & Tricks email by sending a request to Devon Taylor (firstname.lastname@example.org)