実機 (iOS 11.3) でアプリ起動時にクラッシュするのですが、原因が分からず困っています。
(シミュレーターではクラッシュしませんでした。)

クラッシュログの Backtrace に [UIStoryboard storyboardWithName:bundle:] とあるので、
おそらく StoryBoard の読み込みでクラッシュしているのだと思うのですが、
StoryBoard のコネクションをチェックしても問題が見つかりませんでした。

Last Exception Backtrace:
0   CoreFoundation                      0x1837e2d8c __exceptionPreprocess + 228
1   libobjc.A.dylib                     0x18299c5ec objc_exception_throw + 55
2   UIKit                               0x18dd31728 +[UIStoryboard storyboardWithName:bundle:] + 783
3   UIKit                               0x18d793fb8 -[UIApplication _loadMainStoryboardFileNamed:bundle:] + 91
4   UIKit                               0x18d3b1254 -[UIApplication _loadMainInterfaceFile] + 275
5   UIKit                               0x18d37f550 -[UIApplication _runWithMainScene:transitionContext:completion:] + 1411
6   UIKit                               0x18d9afa0c __111-[__UICanvasLifecycleMonitor_Compatability _scheduleFirstCommitForScene:transition:firstActivation:completion:]_block_invoke + 783
7   UIKit                               0x18d37ee4c +[_UICanvas _enqueuePostSettingUpdateTransactionBlock:] + 159
8   UIKit                               0x18d37ece8 -[__UICanvasLifecycleMonitor_Compatability _scheduleFirstCommitForScene:transition:firstActivation:completion:] + 239
9   UIKit                               0x18d37db78 -[__UICanvasLifecycleMonitor_Compatability activateEventsOnly:withContext:completion:] + 723
10  UIKit                               0x18e01372c __82-[_UIApplicationCanvas _transitionLifecycleStateWithTransitionContext:completion:]_block_invoke + 295
11  UIKit                               0x18d37d268 -[_UIApplicationCanvas _transitionLifecycleStateWithTransitionContext:completion:] + 431
12  UIKit                               0x18ddf89b8 __125-[_UICanvasLifecycleSettingsDiffAction performActionsForCanvas:withUpdatedScene:settingsDiff:fromSettings:transitionContext:]_block_invoke + 219
13  UIKit                               0x18df46ae8 _performActionsWithDelayForTransitionContext + 111
14  UIKit                               0x18d37cc88 -[_UICanvasLifecycleSettingsDiffAction performActionsForCanvas:withUpdatedScene:settingsDiff:fromSettings:transitionContext:] + 247
15  UIKit                               0x18d37c624 -[_UICanvas scene:didUpdateWithDiff:transitionContext:completion:] + 367
16  UIKit                               0x18d37965c -[UIApplication workspace:didCreateScene:withTransitionContext:completion:] + 539
17  UIKit                               0x18d3793ac -[UIApplicationSceneClientAgent scene:didInitializeWithEvent:completion:] + 363
18  FrontBoardServices                  0x185fe0470 -[FBSSceneImpl _didCreateWithTransitionContext:completion:] + 363
19  FrontBoardServices                  0x185fe8d6c __56-[FBSWorkspace client:handleCreateScene:withCompletion:]_block_invoke_2 + 223
20  libdispatch.dylib                   0x1830d4ae4 _dispatch_client_callout + 15
21  libdispatch.dylib                   0x1830dc1f4 _dispatch_block_invoke_direct$VARIANT$mp + 223
22  FrontBoardServices                  0x186014878 __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 35
23  FrontBoardServices                  0x18601451c -[FBSSerialQueue _performNext] + 403
24  FrontBoardServices                  0x186014ab8 -[FBSSerialQueue _performNextFromRunLoopSource] + 55
25  CoreFoundation                      0x18378b404 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 23
26  CoreFoundation                      0x18378ac2c __CFRunLoopDoSources0 + 275
27  CoreFoundation                      0x18378879c __CFRunLoopRun + 1203
28  CoreFoundation                      0x1836a8da8 CFRunLoopRunSpecific + 551
29  GraphicsServices                    0x18568b020 GSEventRunModal + 99
30  UIKit                               0x18d68978c UIApplicationMain + 235
31  xxxxxxxxxxx                         0x1004989c0 main + 35264 (SearchViewController.swift:16)
32  libdyld.dylib                       0x183139fc0 start + 3

また NSSetUncaughtExceptionHandlercallStackSymbols しても、何も出力されませんでした。

func application(_ application: UIApplication, willFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey : Any]? = nil) -> Bool {
    NSSetUncaughtExceptionHandler { exception in print(exception.callStackSymbols) }
    return true
}

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    NSSetUncaughtExceptionHandler { exception in print(exception.callStackSymbols) }
    return true
}

他に何かクラッシュの原因を探る方法はありますでしょうか?
何卒よろしくお願いします。

開発環境: Xcode 9.3
開発言語: Swift 4
実行環境: iOS 11.3 (実機)