Hard to say without seeing your calculations and sample data. Please attach a Tableau Packaged Workbook so we can take a look.
I appreciate the willingness to support, unfortunately I won't be able to do that as the data is sensitive, However, it is simply a set of values ranging in price from say $5.00 to $12.00 on the vertical axis, and a set established categories (1-5) on the horizontal axis.
The Calculated field used to introduce the Jitter effect is
IF [Rank]>0 then [Rank] + (([Random()-.05]/6)*[Jitter Effect])
Where the [Jitter effect] Parameter is Binary, Yes (1) engages the random adjustment No (0) disengages it. I believe the heart of the question actually centers around why all values of a given rank are being adjusted by the same random number verse the function in the first picture
Please take a look at the suggested reading on the 'Getting Started' page of the community. It contains a bunch of information on anonomizing your data for upload.
Without a sample, I can't guarantee I'm going to be able to get an accurate representation of what you're seeing. Plus, it's also a bunch of work for me to go ahead and re-create your situation.
You need to create a field that uses the RANDOM() function, then reference that field; otherwise you get the same values.
See this post from Mark Jackson.
(Scroll down to the stuff highlighted in yellow).