Hi Prasad,
It depends on how the strategy Sequence is defined in your valuation variant- if the sequence would be planned price 2 first and planned price 3 is next, then I would think you can check the price validity dates in the material master. The PP2 might not have valid for the valuation date that you are costing.
Hence, it is picked up the price from next sequence.
Hope this answers your question. Please check and confirm.
Regards,
Srinath