iCloud Drive stuck on "Waiting to upload" On both iOS and MacOS, documents in iCloud Drive are never uploaded. Text underneath each document just says "Waiting to Upload"

Already tried turning iCloud Drive off and on again

Any ideas on how to fix this?
Can't speak for macOS, however iOS (iPhone, iPad) iCloud synchronization will be either very slow or just stuck when on a cellular connection. Connect your iOS device to a WiFi and it should sync up almost instantly. This is what resolved my issue with Numbers documents not syncing up on iPhone 6s with iOS 12.1.