Hi @pantelis,
Could you provide us with some additional context on how this is being visualized in the box plot? How are you grouping the data points?
Box plots expect raw values since they distribute the data points out based on the grouping; if you try to run the average of your value, that narrows down to one row and therefore makes a box plot somewhat useless.
Is there another field in your dataset where these rows split which is causing the duplicate rows to exist?
If so, you could try creating a denserank function with that as a dimension, then use that as a filter to only include rank 1.