In BPM's Racks, each part has an "A" button and a triangle-shaped buttons; these are "Auto-Play" and "Play" for controls for loops in Slice mode.

Loops from the factory sounds load in Slice+Map mode by default, and since Auto-Play & Play don't apply in that mode, they will not be available. If you switch to the Edit view, click on the Loop tab, and turn off "Map", you'll see Auto-Play and Play become enabled. 

Additionally, if you are using loops in Sample or Stretch mode, Auto-Play and Play will not be available.