There seems to be a lot of complaints in the past day around the Google Search Console performance report, when the query filter is used on that report. Many are saying when used, the report shows a huge drop in impressions and clicks starting on August 18th.
There is a Google Webmaster Help thread with complaints and several posts on Twitter on this. Here is a side by side, showing the report without the query filter applied and with the query filter applied.
No Query Filter:
With Query Filter:
Google’s John Mueller said he will look into it, but I suspect there is some sort of reporting glitch. John has not yet officially responded about this issue.
Just know, if you see this issue, you are currently not alone.