Why are ad requests and eCPM 0 when the impressions are NOT 0 in the report?

At the moment, ad requests are aggregated on the project level only.
However, impression data is available for ad units and placements levels.
Thus, if you split the data by Ad units or placements, ad requests and fill rate would be 0 for specific Ad units or placements, whereas you should be able to get impression data on ad units or placements levels.