Reads like a classic case of mistaking correlation for causation.
If the upgrade to SPS 10 had caused the issue, then going back to SPS 9 should have removed it again, which wasn't the case.
You write about that the same problem manifests itself in different ways. How do you know it's the same problem?
Without knowing the calculation view design or the planviz files it's not possible to work on this problem.
Not sure why you struggle to "get an answer" from the support colleagues. Typically there would be requests for data to replicate the issue...