1) Your RPD is not modelling sufficiently robustly, and the change in version has caused OBIEE to pick a different execution path for your queries that results in different data
2) Your RPD is perfect, but you have hit a bug in the newer version of OBIEE. In which case, raise an SR to Oracle.
In the clear majority of cases, it's number (1). Your RPD worked beforehand, but only because you were lucky. Take a look at the differences in the SQL being generated, and work it back from there. Work it back to the logical model and understand why the BI Server would be behaving how it is; and then modify the RPD to rectify that.