Continuous Loop or Ping Pong (moving back and forth) playback can be toggled on and off in several ways.
A. Using the Loop/Ping Pong buttons at the side of the play controls.
B. Using the ‘Playback’ option in the 'Navigate' menu.
C. Using the keyboard shortcuts.
Tip: You can also Loop/Ping Pong sections of the timeline by setting In and Out Points.