If there is an application failover during scheduled Salesforce synchronization, the synchronization task remains in running state with status "started". During site initialization, the task is not resolved and only manual deletion of the task will fix the issue. 

using System;
using System.Linq;
using Telerik.Sitefinity.Abstractions;
using Telerik.Sitefinity.Connectivity.Scheduling;
using Telerik.Sitefinity.Scheduling;
using Telerik.Sitefinity.Scheduling.Model;

namespace SitefinityWebApp
{
    public class Global : System.Web.HttpApplication
    {

        protected void Application_Start(object sender, EventArgs e)
        {
            Bootstrapper.Initialized += this.Bootstrapper_Initialized;
        }

        private void Bootstrapper_Initialized(object sender, Telerik.Sitefinity.Data.ExecutedEventArgs e)
        {
            if (e.CommandName == "Bootstrapped")
            {
                StopStartedSalesforceScheduledTasks();
                ResumeStoppedSalesforceScheduledTasks();
            }
        }

        public void StopStartedSalesforceScheduledTasks()
        {
            var startedTasks = SchedulingManager.GetManager().GetTaskData().Where(t => t.Key == SyncTaskBase.TaskKey).Where(x => x.IsRunning && (x.Status == TaskStatus.Started));

            var manager = SchedulingManager.GetManager();
            foreach (var task in startedTasks)
            {
                var taskData = manager.GetTaskData(task.Id);
                taskData.Status = TaskStatus.Stopped;
                taskData.StatusMessage = "Stopped by user";
            }
            manager.SaveChanges();
        }

        public void ResumeStoppedSalesforceScheduledTasks()
        {
            var stoppedTasks = SchedulingManager.GetManager().GetTaskData().Where(t => t.Key == SyncTaskBase.TaskKey).Where(x => x.IsRunning && x.Status == TaskStatus.Stopped);

            foreach (var task in stoppedTasks)
            {
                try
                {
                    SyncTaskLogger.WriteFormat("Resuming stopped scheduled sync task {0}...", task.Id);
                    Scheduler.Instance.RestartTask(task.Id);
                }
                catch (Exception ex)
                {
                    SyncTaskLogger.WriteFormat("Error attempting to resume stopped sync task {0}:\n{1}", task.TaskData, ex);
                }
            }
        }
    }
}