Created attachment 136654 [details]
sheet with pivot table and pivot chart
The current solution of pivot charts uses e.g the structure
<table:table-cell office:value-type="float" office:value="NaN">
to define an identifier for the cell, that will be used in a cell reference.
This structure gives no formal error, but I will surely not support the idea of miss-using a description of a graphical element as identifier for a table-cell.
There exists more suitable solutions.
Currently possible is
as part of the entire table the element
<table:named-expressions> with its child element <table:named-range>.
This problem should be solved together with bug 112783.
I see, that problem has come in earlier and is not specific for pivot charts.
It is already there in LO 3.5.1, but not in AOO 4.1.2. It is not clear, why it was introduced. LibreOffice can handle the chart without having that elements.
Setting to NEW