In some circumstances, hosted feature layer storage is being under-reported, leading to artificially lower monthly storage costs and inaccurate item storage reporting.
This behavior is documented in BUG-000144508, and applies only to hosted feature layers with change tracking enabled and Sync disabled.
The December 2021 ArcGIS Online update, planned for December 8, 2021, resolves BUG-000144508. Organizations with hosted feature layers meeting this condition will see their reporting tools and credit expenditures adjust to include the storage used by their tracking tables.
This may cause Standard Feature Data Store organizations to notice higher monthly costs. The cause of an unexpected increase in monthly costs may be evaluated by viewing the Credits tab on your Organization > Status > Dashboard page over a period that spans the update. If credit costs associated with storage have increased significantly after the update, your organization may have hosted feature layers that meet this condition. Alternatively, if you have an Items report from before the update, it can be compared with one run after the update to identify dramatic changes in a single item’s storage costs.
There is no action required, but organizations may reduce the size of impacted hosted feature layers by disabling change tracking. These settings are explained in greater detail in the hosted feature layer documentation.