Errors are logged as a disk problem, but replace both cables to rule them out and try again, you'll need to do a new config.

Will do.

 

In the Main tab, the list of Array Devices has an Errors column. How much significance should one place on numbers there? Like, does that number include the typical situation of a sector marked as bad and reallocated elsewhere? To my understanding, that is a fairly common occurrence, and only really signifies a failing drive if it starts happening "en masse" (whatever that means).

Those are just Unraid errors, they will reset after a reboot (or if you press the clear stats button).