It could also be that the hard drive has started consuming more power for some reason, more power than the stock AC adapter can supply. If that’s the case then a drive replacement may be needed, or a powered USB hub, or a replacement AC adapter that can provide more power (amps) than the stock adapter (as just mentioned in another posting). Unfortunately there is no easy way to know for sure, just a process of elimination.
@TabloTV maybe consider including a higher amp AC adapter as standard with Tablo units, and/or make a more powerful adapter available on the Tablo website. Could help eliminate many of these issues.