Drive replacement goes into degraded mode w/ inactive drives

So I have a Readynas Nv+ v2 with three drives (in slot 1,2,3). One of the drives failed (in slot 2) so I removed it. System was then running unprotected with no other issues while I ordered a new drive. I installed a new drive (Seagate Barracuda 7200.14 ST2000DM001 back into slot 2) but I am now getting the following error:

RAID sync finished on volume C. The array is still in degraded mode, however. This can be caused by a disk sync failure or failed disks in a multi-parity disk array.

It has now set both Slot 2 & 3 drives to inactive & I have no access to data. System is runnign though. Removing the newly installed drive from slot 2 and rebooting brings the system back unprotected.

I don’t have a PC to connect the new drive to top see if it’s the new drive that’s failing . And why would it take out the drive in Slot 3 anyway if that was the case? I'm more than a little confused...