It involves bullshit DRM and the use of Microsoft Edge. It's not a real hardware issue, but an artificial one to force upgrades. I believe Nvidia cards are now able to do the job now, it's been awhile so I don't recall the exact details.
The other rig is an itx box with a 6700k and I found it insulting Kabylake was just a 6700k with worst thermals and 4K Netflix DRM.
If you want 4k Netflix, I'd skip the PC all together and either get a streaming box or an Xbox One X.