Why are the last scan dates different between the dashboard and device pages?

Sometimes you'll see a different (earlier) last scan date on the dashboard when compared to the site or device pages.

This discrepancy results from the fact that the dashboard relies heavily on 'pre-computed' values.  The dashboard leverages a lot of data, and computing the values that show up in the dashboard is a relatively expensive operation in IDM, so this process runs after scan data is received, and it is further limited to running only once in a 20 minute period. Again this process is relatively expensive, and could take 20 seconds for a small site, with few devices and goes up from there. Large sites will take longer to complete this process, and therefore the discrepancy will exist longer for these sites.

But, there is another consideration as well, pending data.  Pending data is scan data collected by ICE, that for whatever reason, was not uploaded to IDM.  When ICE is again able to upload data, this pending data will be uploaded and on the IDM side processed. So pre-computed values will be generated for the first scan received, but they will not be recomputed until all the pending data is processed.  Pending data is processed one upload at a time, with a 20 minute interval between each.  So for a site scanning every hour, if it's stale for a day, ICE will upload 24 scans, which IDM will process at the rate of one every 20 minutes, meaning, 8 hours of processing time for every day down.

Additionally, when a large amount of scan data is received, there is the possibility that scans will be processed in the wrong order, this is rare, but when it occurs it tends to create spurious stale notifications, these will clear during pending data processing, but can be misleading.
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