Poor quality output using new Hardware Acceleration and h.264
i7-8700K
GTX 1080Ti
Premiere Pro 12.1.1 (Build 10)
After discovering the new hardware acceleration feature I enabled the required BIOS option to allow the UHD 630 graphics to play alongside my 1080Ti, made sure the driver was up to date and found that it works perfectly with my i7-8700K. I then proceeded to render out a bunch of videos to h.264 with a 10mpbs target, enjoying the higher speed and lower CPU load. However when I checked one of the videos I noticed that the quality was extremely poor, despite only changing the hardware/software setting. I re-rendered it using software only and found that to be fine as previously, so it is the hardware accelerated rendering that is causing this. The files are the same size and are otherwise identical so this doesn't make much sense. Here are two screen grabs from the videos, I've made up a little clip in Forza Horizon 3 for demo purposes.
Software Only:

Hardware accelerated:

The difference is clear to see, very poor. As I've said these files are otherwise identical, at least as far as I can tell.
The only different output setting is the software/hardware option. It allows to set a high max bitrate but I can't see that making such a significant difference. For the sake of ensuring I bumped the hardware accelerated output up past 15mbps and it was still poor.
Can anyone shed any light on what's going on or what I'm doing wrong? Thanks
