Based on these findings we activated a similar check and noticed negative impressions (impressions = -1, once -2). This happens in over 10% of our accounts.
<?xml version="1.0" encoding="utf-8"?>
<reportDefinition>
<selector xmlns="
https://adwords.google.com/api/adwords/cm/v201809">
<fields>CampaignId</fields>
<fields>AdGroupId</fields>
<fields>KeywordId</fields>
<fields>Query</fields>
<fields>QueryMatchTypeWithVariant</fields>
<fields>Device</fields>
<fields>AdNetworkType2</fields>
<fields>AbsoluteTopImpressionPercentage</fields>
<fields>TopImpressionPercentage</fields>
<fields>AveragePosition</fields>
<fields>Clicks</fields>
<fields>Cost</fields>
<fields>Impressions</fields>
<fields>Interactions</fields>
<predicates>
<field>CampaignStatus</field>
<operator>IN</operator>
<values>ENABLED</values>
<values>PAUSED</values>
<values>REMOVED</values>
</predicates>
<predicates>
<field>AdGroupStatus</field>
<operator>IN</operator>
<values>ENABLED</values>
<values>PAUSED</values>
<values>REMOVED</values>
</predicates>
<dateRange>
<min>20190411</min>
<max>20190508</max>
</dateRange>
</selector>
<reportName xmlns="
https://adwords.google.com/api/adwords/cm/v201809">
872-671-3425 QueryResult</reportName>
<reportType
xmlns="
https://adwords.google.com/api/adwords/cm/v201809">SEARCH_QUERY_PERFORMANCE_REPORT</reportType>
<dateRangeType xmlns="
https://adwords.google.com/api/adwords/cm/v201809">CUSTOM_DATE</dateRangeType>
<downloadFormat xmlns="
https://adwords.google.com/api/adwords/cm/v201809">GZIPPED_XML</downloadFormat>
</reportDefinition>
Unfortunately I can't show snippets of the resulting report - maybe other fields were negative too.