Windows Server backup failing with "The specified network name is no longer available"

Hello,

I have a Windows 2016 server running Exchange 2016 and trying to do a full backup using Windows Backup to a remote share (shared from another Windows 2019 server). The backup gets to about 75% and then fails with the following:

JobType          : Backup
StartTime        : 20/04/2020 14:13
EndTime          : 20/04/2020 14:19
JobState         : Completed
CurrentOperation : 
HResult          : 8078015B
DetailedHResult  : 80070040
ErrorDescription : Windows Backup encountered an error when accessing the remote shared folder. Please retry the operation after making sure that the remote shared folder is available and accessible.
                    Detailed error: The specified network name is no longer available
JobItems         : {ConsistencyCheckResultList, VolumeList, SystemState, BareMetalRecovery}
VersionId        : 
SuccessLogPath   : C:\Windows\Logs\WindowsServerBackup\Backup-20-04-2020_13-13-52.log
FailureLogPath   : C:\Windows\Logs\WindowsServerBackup\Backup_Error-20-04-2020_13-13-52.log

This keep happening even if I delete the partial backup attempt. There is plenty of room on the remote share around 1TB and i am backing up around 100GB of data.

The Exchange 2016 server is using ReFS drives and can see the remote share, and I can copy large files over it no problem.  The connection never drops.

I have ran chkdsk on both the Windows 2016 server and Windows 2019 server (where the drive is shared) and no errors.

SMB 1.0 is enabled on both servers.

Computer Browser, Server and Work stations services are running.

I have used the ip for the backup job and it still fails.

Any ideas?