If memory serves it's essentially due to licensing restrictions or policy from Netflix themselves rather than there being a problem with Minix. I also seem to recall there being specific instructions on the original forum for installation of a working Netflix .apk
that would at least get you FHD(???). (Hopefully the Minix team or A. N. Other will confirm things &/or correct me but if it helps you look about in the meantime
)...
...The U9-H has the required DRM's in place & it certainly has the specs to stream any FHD/UHD (& HDR) content that Netflix currently offers. Netflix just won't give many of the smaller manufacturers a chance, even if they're a quality brand like Minix. They only begin to consider licensing a product if the number of units being manufactured meets their required minimums. (Ultimately their main interest is in devices from the usual big brand names that have huge production runs into millions of units; that vs a few 100,000 units from a smaller brand name). Mix in the additional variables of how any given device is specifically classified too & it all becomes a bit of a crapshoot. Unfortunately, despite its blatantly obvious intended role as an Android HTPC/TV box the U9-H is still essentially classified as a phone/tablet. It's running a (well) modified version of Android rather than
the Android TV OS.
IMHO, giants like Netflix can easily afford to be selective with their licensing decisions/policies, & it has the obvious kickbacks too. This ongoing cat & mouse game of withholding licensing where there may actually be sufficient demand also allows them to potentially steer consumers back towards the more expensive devices & brand names precisely because they're licensed. Whatever the case, as things currently stand it's a win, win for Netflix!!