WD red 6tb error

My Synology DS216play is giving me the following message: “An unknown error occurred, so hard disk 1 was restarted. If you often see this message, please disable disk write cache.” The hard disk 1 is a WDred 6tb.
What can be the problem?

Beyond testing your hard drive for errors, I would recommend confirming if your NAS has an option to disable the mentioned feature (Disk write cache).