BackupVirtualDeviceFile::RequestDurableMedia: Flush Failure on backup device 'VNBU0-5064-5100' Operating system error 995

Something is going on with a few of my SQL Servers lately.  My SQL Server logs  are filled with lots of the backup error.   For each of my database, there is a set of the error messages like the one below in the SQL Server log and event log every night now.  It is puzzled to me that these errors are generated at a different time each night and I could not find any backup that is scheduled around that time either.  

BackupVirtualDeviceFile::RequestDurableMedia: Flush failure on backup device 'VNBU0-3224-5176'. Operating system error 995(The I/O operation has been aborted because of either a thread exit or an application request.).
Internal I/O request 0x57A37AF0: Op: Write, pBuffer: 0x08460200, Size: 512, Position: 0, UMS: Internal: 0x0, InternalHigh: 0x0, Offset: 0x0, OffsetHigh: 0x0, m_buf: 0x00000000, m_len: 0, m_actualBytes: 0, m_errcode: 995, BackupFile: VNBU0-3224-5176
BackupMedium::ReportIoError: write failure on backup device 'VNBU0-3224-5176'. Operating system error 995(The I/O operation has been aborted because of either a thread exit or an application request.).
BACKUP failed to complete the command backup database "WCS" to VIRTUAL_DEVICE='VNBU0-3224-5176' with blocksize = 512, maxtransfersize = 65536, buffercount = 1

I am attaching the error log for your review.  
ERRORLOG