You may have magnetized part of the frame, or even component leads, confusing the hall effect sensor in the fan.
I would try demagnetizing with the neodymium magnet (or a cassette tape head demagnetizing wand, if such is in your workshop). With the magnet, bring it close to the fan, probably where it was before, then start rotating it and keep rotating it as you back it away from the motor.
I'm not sure the strip magnets are affected much by external fields. I've had fridge magnets near huge nd magnets and still had the appropriate stripe pattern when demonstrating the field viewer for class.