We are seeing that figure on one site only. My main site is consistent with what I would expect, and neither site has had a reduction in ranking on any keywords.
The difference in the two sites is this:
One this is becoming peak market at this time of the year. The other, peak season is off a couple months yet. So, any loss in share of market of Google, or traffic in general, is offset by the growth of the site that is becoming peak. Where the non-peak site, would see the decline.
Having said that, I see no share of market loss for any search engine, on any site. They are all steady at this time.
Also, it has been very hot in the USA. More people at pool side, beaches, and sitting in air conditioned malls. As well, we are in back to school shopping mode here. That has something to do with it. It is close enough now to back to school, that orders online will begin to taper off, as shoppers want the purchases to arrive before kids go back to school. Only 'same day/next day' shipping sites will get heavy orders now.