Cannot Copy Files Larger Than 2 GByte to ReadyNAS

I'm running the latest ReadyNAS 6.9.4hotfix1 on my ReadyNAS with more than 3.5 TByte free and a Windows 10 Pro x64 workstation and have for many years (with whatever the latest official version was at the time).  They are both connected to a GBit full-duplex switch which consistently gives me (and has forever) the theoretical maximum file transfer speeds of 112 MByte/second or so.

 

Now I am trying to do something I've done literally thousands of times before and suddenly it fails consistently: Transferring large files from the workstation to the NAS.  From Windows Explorer or cmd.exe, copying or moving a file works fine at full speed until it hits the 2 GByte point then it stops and errors out.

 

Transferring files between the same drives/filesystems from the NAS to the workstation continues to work regardless of size.  The workstation file system is whatever the current NTFS is and the NAS of course runs btrfs.

 

Am I losing my mind?