How to detect: In the Bent Tube table, the radius of the tube is not as expected. Or in extreme cases, it may be obvious in the 3D View or photo projections.
How to solve: The most probable cause is that tube marks are misreferenced. Check to ensure the Bent Tube marks that are referenced are all of the same real-world tube. Also, check that an incorrect user diameter has not been set in Properties for this Bent Tube.