CallKit Call Directory extension failing with undocumented error code 102

From examining some crashes in crashlytics I can see that for a smattering of users there is a problem occuring when using CallKit's Call Extension, however the error code is one which isn't documented.

The crash is reported as:

libswiftCore.dylib _diagnoseUnexpectedEnumCaseValue<A, B>(type:rawValue:) + 1272

And crash_info_entry_0 is

CXErrorCodeCallDirectoryManagerError(rawValue: 102)

The Apple documentation for CXErrorCodeCallDirectoryManagerError lists the same as in the code (https://developer.apple.com/documentation/callkit/cxerrorcodecalldirectorymanagererror)

And here are the error codes which have values 0 to 8

public enum Code : Int {

    
    public typealias _ErrorType = CXErrorCodeCallDirectoryManagerError

    case unknown = 0

    case noExtensionFound = 1

    case loadingInterrupted = 2

    case entriesOutOfOrder = 3

    case duplicateEntries = 4

    case maximumEntriesExceeded = 5

    case extensionDisabled = 6

    @available(iOS 10.3, *)
    case currentlyLoading = 7

    @available(iOS 11.0, *)
    case unexpectedIncrementalRemoval = 8
}

So what is error 102 and why is it not documented?

Here is my code dealing with the error codes:

CXCallDirectoryManager.sharedInstance.reloadExtension(withIdentifier: Config.callExtensionIdentifier()) { error in
            if let err = error as NSError? {
                self.setLastAttemptToUpdateFailedKey(failed: true)
                if let cdError = error as? CXErrorCodeCallDirectoryManagerError {
                    var debugString = ""
                    var seriousError = false
                    switch (cdError.code)
                    {
                        case .unknown:                      debugString = "Unknown error"
                        case .noExtensionFound:             debugString = "No extension found"
                        case .loadingInterrupted:           debugString = "Loading interrupted"
                                                            seriousError = true
                        case .entriesOutOfOrder:            debugString = "Entries out of order"
                                                            seriousError = true
                        case .duplicateEntries:             debugString = "Duplicate Entries"
                                                            seriousError = true
                        case .maximumEntriesExceeded:       debugString = "Maximum entries exceeded"
                        case .extensionDisabled:            debugString = "Extension disabled"
                        case .currentlyLoading:             debugString = "Currently Loading"
                        case .unexpectedIncrementalRemoval: debugString = "Unexpected Incremental Removal"
                    }