iOS update required - software not found

Every time I connect my iPad Air 2 and my iPhone 6S I get a message that tells me, "A software update is required to connect your iOS device." When I click install I get a message saying it is downloading and then another message which says, "Installation Failed." The software cannot be found on the update server.

iPad Air 2 and iPhone 6S: iOS 12.1.4, 64GB with 37GB free and 32 GB with 20GB free respectively.

Mac Mini: OSX High Sierra, 10.13.6, 8GB, Core i7, 3 GHz