SCCM SQL Backup Failures

[Ann]

Setup:
Single Primary Server: Windows Server 2012 R2
Remote SQL Cluster Server: Windows Server 2012 R2
ConfigMgr version: CB 1810 (KB4490434)

Issue:
Last complete ConfigMgr Maintenance Task Backup was early hours 30/05/2019

Updates installed on the SQL Server: KB4495586, KB4495615, KB4499165, KB4495585, KB4495608, KB4498206, KB4499151.  These were installed on the evening of 30/05/2019

Since last backup on 30/05/2019 the ConfigMgr Backup has constantly been failing with the following messages:
Message ID: 5052, Description: SMS SQL Backup service on the SQL Server *** failed to backup the site database ***, Failed: The error reported by the service is error: CopyFile to *** failed: [error code 2: the system can not find the file specified]. Backup is not complete.
Message ID: 5048, Description: Site Backup Failed while trying to copy the files to the destination. Backup operation is not complete.  Possible Cause: The volume shadow copy service may not have sufficient disk space to create the shadow copy of the site backup snapshot information.

On the SQL Server each time an Event error is created:
EventID: 25, Source: Volsnap, Description: The shadow copies of volume E:\Data were deleted because the shadow copy storage could not grow in time.  Consider reducing the IO load on the system or choose a shadow storage copy volume that is not being shadow copied.

We have rebooted both the Primary and the SQL Servers and also attempted the backup at different times of day.
Has anybody seen this issue before or any advice on best way to resolve this issue? 

[anyweb]

is it shared storage ? " Consider reducing the IO load on the system or choose a shadow storage copy volume that is not being shadow copied. "