Google has posted a note that the Search Analytics report within the Google Search Console might be missing some image search data. This does not mean that you lost any traffic, but rather, the report might show a drop in traffic because of a data bug.
Google said this impacts the Search Analytics report starting on March 24, 2017. Google wrote this only impacts image search, so you might be able to see the drop if you filter the report to show only image search traffic.
Some data for clicks and impressions in image search is being dropped. This is a logging issue, not a traffic issue. We are investigating and hope to have a fix soon.
Again, this is just a reporting bug and should not have resulted from a real traffic loss.
Here is a screen shot showing the “note” in the chart on March 24:
Google has no estimated time for when this will be resolved.
A few weeks ago, you may have seen an image search traffic loss, but that was due to a design change in how Google image search works in specific countries.