OmarNYC, I'm not entirely sure as it's difficult to gauge. At the end of each month when the earnings are reported for delivery, it's around a 1% difference.
For each specific day, I'm not sure. I've only noticed it a few times and Google might be automatically discounting them ,because it only shows on one of the reports and not the others, and disappears quickly (as I said, within 30 minutes). So it's difficult to gauge how many or how often it happens. It doesn't every time I check (not nearly, only a small percentage, like today), just every so often.
I simply find it incredibly weird. We are talking about a 30% difference in that 30 minute time span.