I've heard of cases where technicians have removed the boot drive from a Windows system, connected it as a slave to another system, copied files to it and when the drive is put back into the system, the copied data all disappears. But, I just had a case where we copied 1.5TB of data to a client pre-formatted SATA drive with a couple folders of data on it. We created a new sub-folder and copied all the recovered files there. But, when they took the drive back home and plugged it in, they could only see the folders that were there before we did the transfer. When they brought it back, the only way we could be sure that we didn't somehow mess up was by doing a scan with R-Studio and finding the folder we created.
So, it would appear that Windows 10 file system security measures carry over to more than just the boot drive. But, to what extent, I don't know. Could this happen to external drives too? As I've only heard and seen a very few cases of where this happens, it makes me wonder if there is a security setting that can be enabled or disabled in the OS. Either way, it is super annoying.