It’s possible the one you got is defective. You could contact support about it.
I will say that what you are describing could technically be indicative that the Scale Ultra is more accurate, rather than less. I know that sounds ridiculous, but if you’re curious why I say that, you can read a more detailed explanation here:
I don’t know if or which Wyze scales may use a sort of anchoring or averaging or not, or to what extent. But I do know that the accuracy tolerances for both the original scale and the Ultra are close to the same.
I should mention I am not experiencing these large fluctuations on my Scale Ultra when I step on it multiple times though, so it is possible that you have one that simply has a problem. So I personally would recommend that you contact support because if this was common with the scale Ultra I would’ve expected to have it happen to me too and it’s fairly consistent for me, like never off by more than a couple tenths of a pound at most. So if you are getting over 5 pounds fluctuating, that is worth calling support about.