iOS downloads is one of our core metrics which has been tracked on a regular basis since around 2015 and reported in the Readers team's quarterly metrics meetings and in the Audiences department's monthly readers metrics update.
We saw some artifacts on Nov 13 and 29 2017 from App Annie’s download number, and some spikes from their promotion number in other days. In fact, the units reported by iTunes Connect "Sales and Trends" (when the time zone is set to PST) is equal to the sum of App Annie's downloads and promotions under the "Downloads" tab (see iOS analytics document for more details). And on iTunes Connect, if we breakdown the number by device, we could see those unusual bumps all came from desktop.
Based on our email exchange with App Annie and this discussion on Apple Developer Forums, these downloads from desktop are most likely from Volume Purchase Program, either for educational institutions, or for large enterprises. The way these institutions distribute apps to staff internally is via some form of Mobile Device Management system. There are apps they have to distribute to staff/students, and these apps are purchased in a way that shows up as a desktop purchase in the stats. This makes sense as the person purchasing the apps is most likely sat at a desktop computer putting the order through the system. Unlike a user purchasing and downloading the app, this is like a 'right to download' this many copies of the app, and not actual downloads. See this note for more details.
Although Volume Purchase Program can't explain all the spikes, downloading app on desktop is not a usual behavior, especially since version 12.7 Apple removes the desktop iOS app store. See this announcement and this news article.
Therefore, I suggest we exclude desktop downloads from the iOS app download number we are reporting.