Importing document to app's Document Browser using DocumentBrowserViewController

I've declared a custom export UTI type in a simple Document Based iOS app. I'm now trying to provide the capability to import files of the same type from Mail to the app.

When long-pressing the document icon in the message, I'm given the option to "copy to MyApp" which then calls the method in AppDelegate.m:

- (BOOL)application:(UIApplication *)app openURL:(NSURL *)inputURL options:(NSDictionary<UIApplicationOpenURLOptionsKey, id> *)options {

DocumentBrowserViewController *documentBrowserViewController = (DocumentBrowserViewController *)self.window.rootViewController;
[documentBrowserViewController revealDocumentAtURL:inputURL importIfNeeded:YES completion:^(NSURL * _Nullable revealedDocumentURL, NSError * _Nullable error) {
    if (error) {
        NSLog(@"Failed to reveal the document at URL %@ with error: '%@'", inputURL, error);
        return;
    }
    NSLog(@"Imported document to %@",[revealedDocumentURL absoluteString]);
    [documentBrowserViewController presentDocumentAtURL:revealedDocumentURL];
}];
return YES;
}

However the document is presented, but not imported (the revealedDocumentURL is the same as inputURL, and the delegate method importDocumentAtURL is not called). Maybe I shouldn't be using the revealDocumentAtURL method? I cannot use the importDocumentAtURL: nextToDocumentAtURL: mode: completionHandler: method since I can't specify a document for the nextToDocumentAtURL parameter. Is there a way to import a document to a specific directory? Maybe I'm missing something quite obvious? Also, here's my info.plist file in case it proves helpful.

<dict>
    <key>CFBundleDevelopmentRegion</key>
    <string>$(DEVELOPMENT_LANGUAGE)</string>
    <key>CFBundleDocumentTypes</key>
    <array>
        <dict>
            <key>CFBundleTypeIconFiles</key>
            <array/>
            <key>CFBundleTypeName</key>
            <string>MyApp File</string>
            <key>CFBundleTypeRole</key>
            <string>Editor</string>
            <key>LSHandlerRank</key>
            <string>Owner</string>
            <key>LSItemContentTypes</key>
            <array>
                <string>com.myCompany.MyApp</string>
            </array>
            <key>LSSupportsOpeningDocumentsInPlace</key>
            <false/>
        </dict>
    </array>
    <key>CFBundleExecutable</key>
    <string>$(EXECUTABLE_NAME)</string>
    <key>CFBundleIdentifier</key>
    <string>$(PRODUCT_BUNDLE_IDENTIFIER)</string>
    <key>CFBundleInfoDictionaryVersion</key>
    <string>6.0</string>
    <key>CFBundleName</key>
    <string>$(PRODUCT_NAME)</string>
    <key>CFBundlePackageType</key>
    <string>APPL</string>
    <key>CFBundleShortVersionString</key>
    <string>1.0</string>
    <key>CFBundleVersion</key>
    <string>1</string>
    <key>LSRequiresIPhoneOS</key>
    <true/>
    <key>LSSupportsOpeningDocumentsInPlace</key>
    <false/>
    <key>UILaunchStoryboardName</key>
    <string>LaunchScreen</string>
    <key>UIMainStoryboardFile</key>
    <string>Main</string>
    <key>UIRequiredDeviceCapabilities</key>
    <array>
        <string>armv7</string>
    </array>
    <key>UISupportedInterfaceOrientations</key>
    <array>
        <string>UIInterfaceOrientationPortrait</string>
        <string>UIInterfaceOrientationLandscapeLeft</string>
        <string>UIInterfaceOrientationLandscapeRight</string>
    </array>
    <key>UISupportedInterfaceOrientations~ipad</key>
    <array>
        <string>UIInterfaceOrientationPortrait</string>
        <string>UIInterfaceOrientationPortraitUpsideDown</string>
        <string>UIInterfaceOrientationLandscapeLeft</string>
        <string>UIInterfaceOrientationLandscapeRight</string>
    </array>
    <key>UISupportsDocumentBrowser</key>
    <true/>
    <key>UTExportedTypeDeclarations</key>
    <array>
        <dict>
            <key>UITypeTagSpecification</key>
            <dict>
                <key>public.filename-extension</key>
                <array>
                    <string>myext</string>
                </array>
            </dict>
            <key>UTTypeConformsTo</key>
            <array>
                <string>public.data</string>
                <string>public.content</string>
            </array>
            <key>UTTypeDescription</key>
            <string>MyApp File</string>
            <key>UTTypeIdentifier</key>
            <string>com.myCompany.MyApp</string>
        </dict>
    </array>
</dict>
</plist>

It appears that this was an issue in iOS 11.2. Upgrading iOS to 11.3 and Xcode to 9.3 fixed the problems.