When Remote debugging starts for an iOS device for the first time, debug symbols start downloading. The reasons for the failure may be the following: debug symbols are not prepared for a specific device, symbols storage is inaccessible, the Xcode debug symbols path is not determined or doesn't have enough permissions to create a folder. This issue alone may not prevent you from debugging the device: the symbols will be downloaded after the start of the session when Xcode establishes a connection to the device, but it will take more time.