According to your syslog it look like a couple of disks had connection problems, and then disk11 dropped offline, and later reconnected with a different device ID so it now showing up under Unassigned Devices (Unraid cannot is not hot-plug aware for array devices and cannot handle this so it thinks it has failed).
As was mentioned previously you need to carefully check the cabling (both power and SATA) to make sure all cables are properly seated. Also are you sure your power supply is up to handling all the drives you now have connected?