Check with the motherboard manufacturer.
I asked Asus about this before. But the answer is to ask AMD ....
Max read/write speed of that SSD is around 500-550MBs, so you are well above that mark.
If you have enabled Rapid mode and are scoring less than that, check to see if there is a firmware update available via Samsung Magician. If you need further help, contact Samsung as this is their software and SSD.
I thought i would drop a line of thought , true your max sequential Read speed technically can be 3200mb but that is based on ideal conditions stated officially by Intel.
Why Intel you ask ? Well they are the guys that did the chipset an set the standards on M dot-2 optane technology, which currently is a long way off from ideal speeds. but anyways the low down is this, Both Samsung and Intel have stated the new M.2 3.0 x 4 ssd's are subject to thermal throttling if airflow is inadequate.
Airflow ? really, and most people are still leaning towards mechanical drives, but Samsung itself list Respectively 1800mb for the Evo 960, if the M.2 is to close to the CPU will incure more throttling, basically Optane isn't all that, at least not yet. getting close to 1800mbs with heat and other hard to find issues is pretty dang good if you ask me, an carries 1.5 million hours for it,
How i see it, its the board, as nice as it was at the time , Optane didnt pick up speed untill late 2017, W/o memory or mobo's to support correctly.. in fact M.2 tech been around a few decades now, just been mostly a Wifi port, or for those of us DIY's notebook External GPU port for 20 year old laptops in a closet.
I think your bench mark is hell of a good for what its on.
So i felt i left you in the cold a bit on the topic, so im throwing in a Fix to the whole mess you have found by spending a very substantional amount of dollars .
Your looking at 2 wrenchs in the idea , well 3 considering the mobo, that will need to be corrected. Although your main board like many others starting at mobo's X99 and above support NVe M.2 with onboard slots, your going to still have to get a third party riser PCie xpress cards slot add-on mount cardinto slot. Which brings me to the second wrench a separate thermal Shield and Pad that is compatible to the M.2 card slot you are now mounting into a available PCie x16 slot.
Now even after all that , and bypassing the (very limited ) onbaord M.2 slot, and getting the actaul rated PCIe card slot mounted, and screwed into place... DONT EXPECT EARTH SHATTERING RESULTS.
This is with premium, enterprise grade adpaters mind you, i would start looking into Wings, Angel Wings x4 Adapters, start around 200$ and they kick in a thermal pad.
Hope this helps, i recently looked into this, because i building a new 2017-2018 Mini-itx gaming cube, and i passed on the whole M.2 idea, like as if right?