I think I see part of the problem.
Try going to
http://192.168.100.91yours is going to HTTPS
and these units do NOT use secure
if that isn't it- then my guess is that the drives may very well be bad, and bad in area that the firmware is stored in.
If you're going to downgrade or reflash or wipe the drives to start over:
My suggestion is to take the drives out and put them on a windows machine- and get them surface tested, and then wiped.
Either get your drive mfr testing utilities, or get hd sentinel
www.hdsentinel.com (or something similar) and run a full write surface scan on each disk. I do this for each new disk I put in a NAS, or when this error happens. This way you know if the drive is bad, before you set it up.
There may be a way to do the same kind of test in linux- a full write surface test. But I don't know how that is done.