During synchronisation between SpinPanel and Partner Center, an error may occur if multiple subscriptions with the same offer/SKU are active for one customer. Often this is the case for add-ons. This scenario isn't supported in SpinPanel. Without a unique identification for a subscription, SpinPanel's Partner Center synchronization can not determine which subscription in 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 addon offer: ... Reconcilation is currently only supported when addons with the same offerId are in the same subscription.".
This issue can only be resolved in 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.