DIAGNOSIS The program is likely detecting an overload and backing off the power to protect the motor. This happens if you use too much ice, if the ice cubes are huge, or if the blade assembly is dull.
FIX Use less ice. Don't fill the jar more than halfway with ice cubes before crushing. Also, use standard tray ice, not giant freezer ice chunks or bagged ice that's fused together. Break it up first. Add a splash of liquid (water or whatever you're making) to help get the vortex started.
IF THAT DIDN'T WORK Your blade assembly is probably dull. After a lot of use, especially with ice, the blades wear down. A dull blade can't grab and fracture the ice, so it just pushes it around. Replace the blade & sealing ring assembly.
HEADS UP Never use the tamper to push ice down toward the blades while the machine is running on the ice crush setting. You can damage the blades or the drive socket. The tamper is really for thicker mixtures on lower speeds.