Depending on the the actual part # of your drive, it is possible it won’t accept drives over 2TB each.
Based on interfaces and capacity it sounds like you might have the 0G00273. That was our GEN4 unit and we made a 8TB model 0G02217.
The RAID controller built into the G-RAID is a one time build and cannot be changed for reset. So switching new drives into the enclosure is likely going to result in making it a JBOD enclosure.
I have a similar unit, but part number is 0G00274. Does this particular unit allow drives above 2TB? Also, does it have same limitation in terms of rebuilding the RAID array?