Is there a consistent reason why some POIs may be dropped from Weekly Patterns for a given week? Looking over a period of a few months, we see that some, but not all POIs, will be missing from a week of Weekly Patterns before reappearing the following week: e.g. a POI is present for the weeks of December 6th and 20th but not the week of December 13th. Does this mean that the POI had no visits during the week of December 13th, or are there other reasons for the missing data?
Hi @Peter_Maldonado_Stanford, while a master list does not exist for reasons a POI is dropped. The biggest culprit is usually due to bad SGPID churn – however, what you are describing sounds more like a threshold difference. The POI is not considered dropped unless it is removed from the Core file (reflected in the Release Notes / Change Log).
Basically all patterns poi will be in core, but not all core poi will necessarily be in patterns.
If you are seeing points disappear in patterns, it is relatively safe to assume they had no visits
More information on Drops can be found here:
Excerpt from March release notes:
Drops 
We ingest data from many sources, and due to source changes and processing changes, Placekeys churn over time. In this release, we dropped 32,779 Placekeys (14,826 branded and 17,953 non-branded).
Major reasons for drops:
• ~1k dropped as result of improved deduplication
• ~2k dropped as a result of bug fixes for branded POIs
• ~6k dropped due to address encoding changes
• ~15k dropped due to changes to the Where part
To keep track of the status, predecessors, and latest successor of each Placekey, try using the new Lineage API.