This is a limitation we put in to avoid having a chart spend too much time fetching data.
The current limit is for a stacked bar chart is at 10,000 elements visible on screen, then we will render the amount of data we haven't fetched as one "bucket". If you add in a dimension limit or reduce the amount of segments they will dissaperar.
Could this be the Sense equivalent of the QV "Set Reference" option (on the right click context menu). This creates a shadowed/grayed out version of the data using one set of selections and allows you to make another selection to compare to the reference version?
In QV, you remove the reference line with "Clear Reference".
Logic will get you from a to b. Imagination will take you everywhere. - A Einstein
Due to not having this option in QS i don't think so, but even this would be an option in there, why does it happen automatically only on this chart? i made several other ones similar to this and it did not happen there.
Had the same problem two to three weeks ago, but i thought it was due to the set expression, but i wasn't sure.