@phillxnet OK I have managed to install Rockstor 4 on a test NAS which is an partially empty Thecus N8900 (same model as above). I am able to add the previous NAS without the duplicate key error, however, this is because the new version 4 uses lower case instead of upper case.
3.9 : 5C4606FA-192F-453A-B299-7B088C63BB9B
4.0 : 5c4606fa-192f-453a-b299-7b088c63bb9b
I think therefore you need to update your file /opt/rockstor/src/rockstor/system/osi.py to include lower case versions, as it’s obviously not triggering whatever process is required to generate a properly unique ID for the system. I also did flash the latest bios for this device, so maybe that providers a lower case return from /sys/class/dmi/id/product_uuid, or maybe it’s OpenSUSE vs Centos.