Diagnosis
The lid sensor is not detecting the lid correctly. The magnet in the lid handle or the sensor in the pitcher collar is misaligned or failed.
How to Fix It
First, ensure the lid handle is fully rotated clockwise to the lock position. You'll feel a click. If it still flashes, remove the lid. Check the small rectangular magnet inside the plastic of the lid handle. It should be flush. Clean any debris from the sensor area on the pitcher collar. Re-seat the lid firmly.
If That Didn't Work
The sensor in the pitcher collar itself may be faulty. This requires replacing the entire pitcher collar assembly. Contact Ninja Customer Support for a warranty replacement of the pitcher.
Heads Up
Do not attempt to bypass the lid sensor. The blender will not operate without it for safety reasons. A damaged pitcher collar is not user-serviceable.