Cin7 fulfilments not updating to Amazon

We are operating a FBM seller account with Amazon, and using ShipStation for our fulfilment from Cin7.

We have an issue where sometimes the fulfilment tracking updates to Amazon, and sometimes it does not and we have to manually add the tracking in Amazon (which is critical to maintain our seller rating).

Does anyone know why the fulfilment updates to Amazon might not be working? I don't see any errors in the Amazon integration logs.