This is a not a hardware issue of the NAS. It is a known QES firmware issue on TES-1885U/TES-3085U. It recognizes the REXP-1220U as a REXP-1620U unit which is wrong.
If you are using QES firmware, please wait for the latest firmware to solve it.
(The QES firmware version must be later than 1.1.4 build 20170908.)