Maybe someone has a better answer but my gauge moves around as the road changes. When going uphill or downhill the gauge pointer changes with the grade.
I don't recall seeing the pointer jump on a bump but I'm not sure I've ever looked at the gauge while going over a bump.
If an up or downgrade moves the pointer, I wait till I get back to level ground to estimate the fuel level.
I always assumed this was normal since the gauge sender is a float and moves about as the fuel sloshes back and forth according to the road grade.
If your pointer jumps but returns to a correct level, it doesn't seem to be a serious problem.
If the pointer stays in a "jumped" position then more advice is needed here. The float might need to be removed and cleaned or possibly replaced...wait for others to comment...and be sure to use a brass tool to loosen the float compartment cover...a spark would be most unwelcome.
Richard M, NYC