If you look at the HW (hardware errors) column, the number there is huge for the 2-day mining period. One of the chains (likely the low-temperature one) is having trouble. I have an S3 that behaves similarly and gets similar numbers; the hashrate is just slightly above 1/2 nominal (meaning 230-250).

If you reboot it, you may find that it hashes fine for a few minutes then one of the chains will start acting up again and your hashrate will drop. When this happens you'll see the HW number start going up. For my unit, I took off the case and removed the 2 externally-facing heatsinks to see if it was making good contact with the chips. It seemed fine, but I re-applied thermal compound and re-installed the heatsinks. This didn't make any difference.

What I ended up doing is UNDERCLOCKING the unit. Try 212, and lower if you have to. It can help if you power the unit down completely for a few minutes to let it cool down. I got my unit running at 395GH/s for about a day before HW errors started spiking again. I underclocked it further and it has been stable now for a few days.

YMMV.