DIAGNOSIS The machine's sensor is still detecting a mineral buildup, usually in the internal tubing or around the heating element. Vinegar sometimes isn't strong enough if your water is very hard.
FIX You need a proper descaling solution. Here's the drill: 1) Fill the reservoir with a full bottle of Ninja-approved descaler and water to the MAX line. 2) Put a large carafe on the drip tray. 3) Run a full Hot XL cycle. 4) Let the solution sit in the machine for 30 minutes. 5) Run two more full Hot XL cycles with just fresh water to rinse it all out. That should clear the sensor.
IF THAT DIDN'T WORK There's a small chance the float sensor in the reservoir is stuck, tricking the machine into thinking it's empty during the cycle. Unplug the machine, pull out the reservoir, and check the little white float on the bottom. Move it up and down a few times to make sure it's not jammed.
HEADS UP Never use descaling solutions in the Cold Brew function—it's only for the hot water system. Running it through the cold side can damage the internals.