It is possible to see the error if you have forgotten to include the proper "Privacy" entry in your info.plist file.

For iOS 13+, add the "Privacy – Bluetooth Always Usage Description" to your info.plist file.

For iOS 12 and lower, use the "Privacy – Bluetooth Peripheral Usage Description" to your info.plist file.

Additionally, be sure that you have selected the "Background modes" option for "Uses Bluetooth LE accessories".