VSE interpolation error

Hi, i have found weird issue in blender VSE. Sometimes when animating offset of an object its interpolation in graph editor is very weird step like curve (on the left screenshot) normally it should be smooth like on the right, problem is not only display of the curve, the object is animated in jittery, shaky way instead smooth.

I am recreating this curve all over again and still same error ocurs, what can be the problem?

thanks in advance ror any advices