Slow copies are sometimes caused by multiple read/write errors (the software is designed to keep retrying in the background when these happen), or more likely a Windows security setting issue.
 
Windows has a built-in security mechanism called Windows Defender. And while this is a great tool for protecting your computer from unwanted viruses and such under normal use, it can cause slow transfers for offloading as it examines each file for viruses, etc. This is where 'whitelisting' comes in. It's a setting under security preferences to tell the operating system that certain applications and mounted drives can be trusted and don't need continuous scanning.
 
It's also possible you have “semaphore timeout” errors if you're attempting to copy to a RAID or network storage. This is a common network file transfer error, likely related to a firewall or virus protection.
The solution is to whitelist the application by adding it to the security exclusions and the output destination(s).
 
To do that:
 
1) Launch the Settings App in Windows 10
2) Go to "Update & Security"-> "Windows Security" -> "Virus & Threat Protection" -> "Virus & Threat Protection Settings (Manage Settings)"
3) Scroll down to "Exclusions" and click "Add or remove exclusions"
4) Click "Add an exclusion" to add an exclusion to Windows Defender for the following items.
     4a) Select "Process" and enter "ShotPutPro.exe"
     4b) Select "Folder" and then select the root drive letter of the RAID.
 
Here's more information about semaphore timeouts
 

[Also, there is a known issue with some older versions of Windows 10 that may cause slow copies. Be sure to update Windows 10 to latest available version.]