In a post from Google, there is a data anomalies bug involving the Search Analytics report found in the Google Search Console.  The specific issue shows up when using the “AMP non-rich results” search appearance filter and look at the clicks and impressions between December 14, 2017, and December 18, 2017.

According to Google, there “was an error in counting AMP non-rich results impressions and clicks” between those dates and you “might see a drop in your data during this period.” It did not impact the actual search results; it was just an analytics bug.

The following could be what the report could look like for you:

The data should be returning to normal on or after December 19, 2017.  Those few days will have some inaccurate data.