Personally I wouldn't use that NAS for storing data until figuring out what went wrong, since every single file was corrupted. This is way too high an error rate and unlikely to be caused by a hard drive or network issue. It's probably an issue caused by NFS/SMB/... client/server bugs.

Edit: Quick googling finds many people using Macs report files are corrupted when written to a Synology NAS over SMB.