Tips on troubleshooting Subscription issue in Reporting Services
1 – Look at the Reporting Services Log File
  Error Message from Log File:
 Email Provider has no server or pickup directory specified, Microsoft.ReportingServices.Diagnostics.Utilities.ServerConfigurationErrorException: The report server has encountered a configuration error. ;
  ERROR: Throwing Microsoft.ReportingServices.Diagnostics.Utilities.ServerConfigurationErrorException: Email Provider has no server or pickup directory specified, Microsoft.ReportingServices.Diagnostics.Utilities.ServerConfigurationErrorException: The report server has encountered a configuration error. ;
  INFO: Notification 20f7b482-eb74-4b51-9e53-9f0609034e72 completed.  Success: False, Status: Failure writing file Startup : The report server has encountered a configuration error. , DeliveryExtension: Report Server FileShare, Report: Startup,
 …….
    2 – Run below query against ReportServer Database and this query will give you Subscription job details which are scheduled and history of when it was last run
  select
 ‘SubnDesc’ = s.Description,
 ‘SubnOwner’ = us.UserName,
 ‘LastStatus’ = s.LastStatus,
 ‘LastRun’ = s.LastRunTime,
 ‘ReportPath’ = c.Path,
 ‘ReportModifiedBy’ = uc.UserName,
 ‘ScheduleId’ = rs.ScheduleId,
 ‘SubscriptionId’ = s.SubscriptionID
 from ReportServer.dbo.Subscriptions s
 join ReportServer.dbo.Catalog c on c.ItemID = s.Report_OID
 join ReportServer.dbo.ReportSchedule rs on rs.SubscriptionID = s.SubscriptionID
 join ReportServer.dbo.Users uc on uc.UserID = c.ModifiedByID
 join ReportServer.dbo.Users us on us.UserID = s.OwnerId
 join msdb.dbo.sysjobs j on j.name = CONVERT(nvarchar(128),rs.ScheduleId)
   –This query will help you to investigate further
 select
 ‘Report’ = c.Path,
 ‘Subscription’ = s.Description,
 ‘SubscriptionOwner’ = uo.UserName,
 ‘SubscriptionModBy’ = um.UserName,
 ‘SubscriptionModDate’ = s.ModifiedDate,
 ‘ProcessStart’ = dateadd(hh,DATEDIFF(hh,Getutcdate(),Getdate()),n.ProcessStart),
 ‘NotificationEntered’ = dateadd(hh,DATEDIFF(hh,Getutcdate(),Getdate()),n.NotificationEntered),
 ‘ProcessAfter’ = dateadd(hh,DATEDIFF(hh,Getutcdate(),Getdate()),n.ProcessAfter),
 n.Attempt,
 ‘SubscriptionLastRunTime’ = dateadd(hh,DATEDIFF(hh,Getutcdate(),Getdate()),n.SubscriptionLastRunTime),
 n.IsDataDriven,
 ‘ProcessHeartbeat’ = dateadd(hh,DATEDIFF(hh,Getutcdate(),Getdate()),n.ProcessHeartbeat),
 n.Version,
 n.SubscriptionID
 from Notifications n
 join Subscriptions s on n.SubscriptionID = s.SubscriptionID
 join Catalog c on c.ItemID = n.ReportID
 join Users uo on uo.UserID = s.OwnerID
 join Users um on um.UserID = s.ModifiedByID