Looks like Fabric is recalculating or correcting the count for one of my events (iOS app) 6-12h later. The updated count is always lower, 20-30% down.
Mike from Fabric here. Yes, this can happen either for a count upward or downward around UTC midnight each day.
We have two layers of processing - speed and batch - that allow us to collect data in real-time, while at the same time correcting any errors that happen during the collection of the data. What you're seeing happen is the correction of the speed data layer by the batch layer.
As a result of having less time to calculate speed layer information we use probabilistic algorithms which let us calculate this information in real-time, but a cost of reduced accuracy. For most apps, the correction is extremely small, but there are outliers.