Q: hfs_clonefile: cluster_read failed: -34

Hello, ever since updating to El Capitan, I'm getting a ton of these "hfs_clonefile: cluster_read failed: -34" errors in my Console logs. I have a Late 2009 27" 2.8 GHz iMac booting off of a new 4 TB Seagate SSHD external firewire drive in a NewerTech miniStack Max enclosure. I have 32 GB memory and I'm running OS X 10.11.5.

Other than an occasional kernel panic, I haven't been able to pinpoint any noticeable performance issues, though any disk errors are always a little disconcerting. I'm mainly curious as to what would be causing this behavior, as there appears to be very little information out there on -34 errors. I do wonder if this is somehow associated with permissions errors and/or Spotlight indexing, but it's hard to tell from the logs.

This is a brand new drive, and I've already had both the drive and enclosure replaced. I've also tried replacing the Firewire cable, and there's only one FW800 port on this machine. I do need the speed of this connection since I'm using the drive as an external boot. I get this error, regardless of whether there are any other devices connected to the FW800 chain or USB, i.e. the error appears if the disk is the only thing connected. I've tried many other strategies without results, including resetting PRAM, NVRAM, booting into Safe Mode, Recovery Mode, reinstalling OS multiple times, erasing and reformatting drive, Disk Utility repairs, etc. At one point, I rebuilt some caches related to an lsd folder. That seemed to help with some other errors that were being generated, but not with the hfs_clonefile errors.

Finally, I'd also note that this is a hybrid drive, so I doubt TRIM is an issue. And I'm only getting -34 errors, not the more common -5 errors or i/o errors that seem to accompany a failing disk drive.

Any insight or help would be greatly appreciated. Again, I'm mainly curious as to what a -34 error means, and whether I should be worried about the integrity of the external drive.