What is the cause of ERROR 1327 "Account restrictions are preventing this user from signing in..." when ROBOCOPY is copying files?

I am using ROBOCOPY to copy some files from a remote share to a local folder on a server. The file set is fairly large (about 500,000 files). The copy process starts and runs successfully for an hour or two and then ROBOCOPY starts reporting an error on every attempted copy. The errors are just like this except for different folders:

2019/02/22 08:22:16 ERROR 1327 (0x0000052F) Accessing Destination Directory E:\PDM_DATA\PDMVaultTest\0\000cfa40\

Account restrictions are preventing this user from signing in. For example: blank passwords aren't allowed, sign-in times are limited, or a policy restriction has been enforced.

The ROBOCOPY command line I am running is: ROBOCOPY \\REMOTESERVER\PDM_DATA\PDMVault E:\PDM_DATA\PDMVaultTest /mir /r:1 /w:1 /log:E:\PDM_DATA\CopyPDMVaultFromProduction.log

I'm logged into the server with local admin credentials and running the command prompt with the Run As Administrator option.

Update

I tried running this same copy operation with a program called SyncBackPro. That program was very slow and the same error message occurred as with ROBOCOPY.

However, when SyncBackPro reported the error it clearly indicated that it was failing when trying to read from the remote share. The remote share is on a virtual server hosted on AWS which is joined to our domain. I suspect that the slower wide area network connection that is required to communicate with the AWS host from the on premises destination server is the likely cause of my problem.

I did give the /b option with ROBOCOPY a try but that did not help.