R31804 give unaccurate variance depend on data selection

[dums2]

Hi every one, we are on JD Edward ERP8 Sp22 and we experience some problems with the R31804. When we run the report on a WO that has no variance at all, we received different result for it depend on data selection. If we run only on that WO, we may have all the WO value as variance. If we change the data selection to run on 2 or 3 WO, the report don't give the same result.
If we put the PPFG flag in my data selection.

Does someone could help us...