Google posted there is a bug/error with the Google Search Console's Search Analytics report that has assigned all your traffic in the devices section to be from desktop origin, as opposed to the mobile or tablet.
The bug is still open, but they are actively working on fixing this. Google wrote, "On July 29 all traffic in Search Analytics began to be erroneously categorized as "Desktop" traffic in the "Devices" grouping category. We hope to fix this issue shortly."
It is hard to replicate, as many Search Console reports do not let you even see July 29th data yet.
So I guess Google has a bit of time to fix the issue before webmasters see it?
In any event, Google wanted you to be aware of this issue.
Forum discussion at Google+.
Update: Google said the "mislabeling was corrected on Aug 1."
