[Aside: Do not worry about it saying "Manufacturing Mode". This is a necessary step in the factory during the preparation of a new unit (though they are supposed to exit it from this mode before shipping). Regardless, after a number of reboots, it will exit this mode on its own and you will see it stop presenting this message. From an operational standpoint, this means nothing to the end user.
My gut reaction to this happening with a new NUC is that there is something wrong with one of the other components being installed into it. Usually, this is caused by a marginal/failing SODIMM. Since the graphics engine uses conventional memory for its buffers, it is not uncommon to see the graphics engine failing to initialize when such a SODIMM is present.
[Aside; The fact that you might have passed a memory test, even one hours or days long, is not a guarantee that there are no issues in the memory. I have a SODIMM that has passed many days of testing with MemTest86+ yet I know for a fact that it is bad and that every NUC I put it into will (eventually) have problems as a result.]
Bottom line, I recommend that you test the unit with different memory (borrow it if you can). If this alleviates the problems, you will know the older SODIMM(s) were the culprits.
Hope this helps,