Okay, loading or not loading kmod-usb-storage-uas makes no difference: you are not able to use your ssd as storage device.
Last idea: when you connect your ssd to a normal PC, does the ssd (with usb enclosure) work with or without the uas driver? If the ssd works with a PC, then (that's my personal conclusion) the mess is with the MR8300 router (hardware and/or software). Or did I miss anything?