When using a UNNotificationServiceExtension, Apple gives you 30 seconds to do your downloading / processing for the notification before it drops the hammer.
Take downloading an image to be used in the rich notification for example...
Say I spend 20 seconds downloading and processing an image.... during which 2 more notifications for my app come in, plain text so they don't trigger the notification extension.
Will the OS block these until I'm done processing my first, so that they appear in order?
notification extension processing runs in serial... so notifications are always delivered in order... and the code for the next one doens't even start running until after the one before it is completed and delivered