DeviceSync how to check with Swift SDK if all server changes have been received?

I am migrating my Application data from Simperium to Realm with Atlas Device sync. Since I’m not interested I migrating inactive users and devices, I decided to do the data transfer via the App. The user opens an updated App, the App migrates the data, marks the device migrated, done. However it turned out Simperium might have messed up some datasets, so some devices might have slightly different data for the same user. So the idea is , if the user opens my App on a second device, it is to wait for DeviceSync to finish downloading data, then try to migrate anything that was not done from the original decide. All is working except I can’t figure out when a current session is done downloading changes. Any Help?