You can check by parameterizing your inputs and outputs.
For example, in mesh window, you can paremeterize number of element, nodes, orthogonal quality (or which one do you want for mesh quality)
If your results are dependent on specific location on geometry, paremeterize that location mesh settings, too. ( like bias factor, number of elements or something else)
for setup, you can do same thing for your inputs and outputs like inlet velocity, output temperature, pressure, Gr number etc.
With this, you can change your mesh and see the both mesh quality and result change using parameter set window. This can be a way to compare mesh quality with results.
Maybe your simulation needs low aspect ratio, reason for fail may comes from this.
Maybe your formulations for results are not proper, I am not expert on this formulation but I have been working on to understand method in ansys, too
As far as I know huge differences or sudden changes in solution part is about mesh quality. Mesh transition should be smooth, especially for sensitive calculations like heat transfer applications.