If the drives are larger than 2GB and they are formatted as GPT, and your W10 computer has a bootdrive (C: drive) formatted as MBR which it would be from the factory if that HDD is <2TB in most cases, the files are being copied from a drive with an incompatible file format (GPT) trying to be read on your W10 computer which is running MBR. That's most likely the reason why you have rename the file in your MBR drive in order to preview/open the file.
You (or your Customer) have 2 choices:
1.) Backup all the data on your (their) NAS device elsewhere such as to the Cloud or another external drive, clear the NAS and reformat it in MBR format. Restore the data back on to it. Retest your file copies.*
2.) Do a Clean...