Hi,
we observe a similar behavior at KEYWORDS_PERFORMANCE_REPORT.
Our RequestFields are "AdGroupId", "Id","KeywordText","KeywordMatchType" and "QualityScore" (no segmentation) and we set IncludeZeroImpressions to FALSE.
Since October these reports are empty, but if we include the field "Impressions" in our Request, everything worked fine.
It seems, that we now must include all Fields, that we filter on.
Jam