I think you are on the right track.  I see no CRC errors so its SATA cable (if any) is probably fine, but the connections are clearly loose somewhere.  The drive dropped off completely several times, and was disabled (so your reboot was needed).  I'd very carefully check and reseat both the SATA connections and the power connections, all the way back to their source, especially any power splitter.  Something is loose.  I suspect if you had been close, you may have heard the drive cycling up and down (if the power connection was loose).

Thanks guys.  The setup has been running fine overnight and sab has been flat out downloading to the cache drive without issue. So perhaps just a bad connection. Thanks again des.

Just a follow up guys. I had the same issue come back again a few times. On the last time I was ready with a 250gb ssd to replace the seagate cache drive.  So I swapped drives and upgraded to unraid version 6 with the cache drive formatted as xfs. I also noted my 5 v rail was at 4.85 volts so swapped my pico psu for another better pico unit. Anyhow I have had no issues since and if I am copying to my cache drive at the same time as sabnzbd is working I get no slow downs. The new docker system seems cool too.

 

The issue was probbibly a combo of iffy psu and hard disk.

 

 

Thanks des.