I had the same "Failed to Decrypt data" issue with SharePoint 2016. After opening a support case with Microsoft we found that the server was unable to decrypt the DistributedCache key within the registry here:
HKLM\SOFTWARE\Microsoft\Shared Tools\Web Server Extensions\16.0\Secure\Credentials
The Solution was to rename the "Credentials" key then reboot the machine. After the reboot, the "Credentials" key will be automatically recreated. Confirm that the correct permissions are set for the "Credentials" key after the reboot:
The permissions should be: WSS_WPG – Read, WSS_ADMIN_WPG - full control
If the permissions were not correct you, you will need to correct them and then reboot again.
I can confirm that after this I no longer received any Event ID: 6398 Errors in the Application event log.