The workflow has ended unexpectedly. An error has occurred in [x].

Hi Andrew,

Thanks for your reply! We were able to resolve it without Nintex Support. I also forgot to mention a few details in case this helps someone in the future:

Symptoms:

1. This happened to a site workflow, not a list workflow.
2. As far as workflow actions go, I have zero delays/pauses/”wait-until” in the workflow. However, the error is generated with a time stamp that's 1-2 minutes after the entire workflow completes successfully (i.e. after all workflow actions are completed). It always errors at the end.
   
   

               Workflow Messages

               Time: 11/13/2015 1:47 PM

               Event: Error

               Message: An error has occurred in [workflow name].

               Outcome: (empty)

      3. See the ULS logs below. This is the error: "List does not exist.  The page you selected contains a list that does not exist.  It may have been deleted by another user."

Solution:

1. In a nutshell, the fix was to add the workflow action called "Commit pending changes" inside one of the For Each loops. A colleague had a hunch that "Commit pending changes" could resolve it. To test the hunch, I added the action after every variable or update action in the workflow, and then narrowed it down to just one spot in the workflow.

Screenshot of the workflow fix:

ULS log associated to the workflow instance:

Name=Request (GET:https://<siteURL>/_layouts/15/NintexWorkflow/preview.aspx?ListId=00000000-0000-0000-0000-000000000000&ItemId=-1&WorkflowId=7a788886-655f-444e-bd8c-aa3ef6eb225x&mode=Runtime&InstanceId=6e766509-vec5-4j88-bcfd-7sw55ded432b)

List does not exist.  The page you selected contains a list that does not exist.  It may have been deleted by another user.

SPRequest.GetListsWithCallback: UserPrincipalName=i:0).w|s-1-5-21-118107795-1152602752-1039283242-867337, AppPrincipalName= ,bstrUrl=https://<siteURL>/_layouts/15/NintexWorkflow/preview.aspx?ListId=00000000-0000-0000-0000-000000000000&ItemId=-1&WorkflowId=7a788886-655f-444e-bd8c-aa3ef6eb225x&mode=Runtime&InstanceId=6e766509-ceb6-4f74-bcfd-7da50ded432b ,foreignWebId=00000000-0000-0000-0000-000000000000 ,bstrListInternalName={00000000-0000-0000-0000-000000000000} ,dwBaseType=-1 ,dwBaseTypeAlt=-1 ,dwServerTemplate=-1 ,dwGetListFlags=0 ,dwListFilterFlags=4294967295 ,bPrefetchMetaData=True ,bSecurityTrimmed=True ,bGetSecurityData=True ,bPrefetchRelatedFields=False

System.Runtime.InteropServices.COMException: List does not exist.  The page you selected contains a list that does not exist.  It may have been deleted by another user., StackTrace:    at Microsoft.SharePoint.SPListCollection.EnsureListsData(Guid webId, String strListName)     at Microsoft.SharePoint.SPListCollection.ItemByInternalName(String strInternalName, Boolean bThrowException)     at Microsoft.SharePoint.SPListCollection.GetListById(Guid uniqueID, Boolean bThrowException)     at Microsoft.SharePoint.ApplicationRuntime.BaseApplication.Application_PreRequestHandlerExecute(Object sender, EventArgs e)     at Microsoft.SharePoint.ApplicationRuntime.SPRequestModule.PreRequestExecuteAppHandler(Object oSender, EventArgs ea)     at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()     at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)     at System.Web.HttpApplication.PipelineStepManager.ResumeSteps(Exception error)     at System.Web.HttpApplication.BeginProcessRequestNotification(HttpContext context, AsyncCallback cb)     at System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context)     at System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(IntPtr rootedObjectsPointer, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)     at System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(IntPtr rootedObjectsPointer, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)     at System.Web.Hosting.UnsafeIISMethods.MgdIndicateCompletion(IntPtr pHandler, RequestNotificationStatus& notificationStatus)     at System.Web.Hosting.UnsafeIISMethods.MgdIndicateCompletion(IntPtr pHandler, RequestNotificationStatus& notificationStatus)     at System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(IntPtr rootedObjectsPointer, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)     at System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(IntPtr rootedObjectsPointer, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)