DIAGNOSIS The blender isn't achieving full power, usually because it's overheating and the thermal protector is kicking in, or the drive connection is slipping.
FIX First, rule out technique. For hard frozen items, use the Pulse function in short bursts to break things up before holding a continuous speed. Don't just dump a full jar of solid frozen chunks and hit High. If technique isn't the issue, check for overheating. Feel the base of the unit after it struggles. Is it very hot? If so, you're likely overworking it. This blender has powerful motors that can overheat with extended use on tough tasks. Let it cool down completely (30 minutes). For your next blend, use shorter cycles with pauses.
IF THAT DIDN'T WORK Inspect the drive coupling. Unplug it, remove the jar, and look at the black plastic square peg on the base and the matching socket on the jar. If the corners are rounded or there's black plastic dust, the coupling is stripping and slipping under load. This requires a base repair.
HEADS UP These are high-performance blenders, but they're not industrial machines. Pulsing is your friend for dense loads. Continuously running an overheated motor will eventually cause permanent damage.