A snap roll is when ONE WING STALLS before the other. [ Usually at the tip. ]This produces an unbalanced lift condition and the model rolls very quickly through 90 to 180 degrees.

This is a desireable characteristic if you are a full size competiton / disply piolot but not for a low air time modeller.

Some of the ARTF Caps can be heavy and are prone to doing this on the landing approach and on high G turns.