What is the name for the situation where Parallel paths (and fuzzy solutions) are created when unnecessary physical joints are included in the idealised model.  e.g. two hinges on a door, or a forked link rod.

I have 2 equal and opposite forces acting on a floating body.  Part way through the timeline, and in the absence of any excitation, the plots of the forces transition from both pushing to both pulling, and pass through zero magnitude in the process, which is nonsense.  The after transition magnitude is clearly less than the before transition magnitude.

How do I convince a disbelieving auditor that the results of my analysis are nevertheless correct?