StoreKit's SKStoreProductViewController takes very long to load an app on iOS 12. Like 12 seconds long :-(
There must be a bug in there somewhere, and the only thing I can find in the console are these two lines that are printed just before the long wait:
Sep 18 10:24:03 ProductPageExtension(AppStoreDaemon)[3386] <Notice>: [AppStoreKit.UpdateStore]: We have the entitlement: com.apple.appstored.xpc.updates result: 1
Sep 18 10:24:03 ProductPageExtension(AppStoreDaemon)[3386] <Notice>: [AppStoreKit.UpdateStore]: getUpdatesWithCompletionBlock
I have filed a radar. http://www.openradar.me/radar?id=4990591884591104