Often this error occurs due to add-ons. This scenario isn't supported in SpinPanel. Without a unique identification for a subscription, SpinPanel's Partner Center synchronization cannot determine which subscription in the Partner Center is which subscription in SpinPanel and therefore is unable to update the correct subscription in SpinPanel.
If this error occurs it will be shown in the service health log (Health > Service health) and look something like this: "Multiple subscriptions detected for the add-on offer: ... Reconciliation is currently only supported when add-ons with the same offerId are in the same subscription."
This issue can only be resolved in the Partner Center by manually increasing the quantity on the subscription and/or add-ons on one specific subscription and decreasing the quantity of the other subscription to one and suspending it.
I.e.: Subscription A has a quantity of ten and five add-ons. Subscription B has a quantity of ten.
Increase the quantity on Subscription A to ten, decrease the quantity on Subscription B to one and suspend it. Afterwards the Partner Center synchronization will import Subscription A with a quantity of twenty, including the five add-ons as well.