A 1070 is not that powerful
The 1070 is more than enough to decode 8 bit h.264, and it can h.265 just fine too. It has nothing to do with the card, it has everything to do with how the data is send to the card. Also, the Windows panel is consistent: when the gpu is not activated, the cpu is, big time. So it's not a Windows bug. Windows reports it just right.
It's funny how many comments are over here to try to make me sound that I did something wrong, or that I don't know what I'm talking about. The bug (or weak architecture) is real, and it's either Resolve's, or the driver's. And my money is on Resolve.
You simply cannot decode a random frame that is part of a GOP sequence, you have to decode many frames and sometimes even all frames.
It's not "many" frames, it's a few frames. And Resolve could easily send the data to the card starting from the "right" frame before it, and then display the video from the frame the cursor demands of it. Either way, this is something to be fixed, and it can be fixed. Before I became an artist I was a programmer, so I can distinguish between weak code and an "impossibility" as you present it.
It's unacceptable to be buying the Studio version with the promise of hardware accelerated h.264/5, and having it work only "some times". VLC and other players I tried DO NOT exhibit such a behavior.
If you can discern a pattern, you could maybe help the developers solve this, but other than that, just wait.
It's 100% reproducible. All they have to do is put some h.264 and h.265 files on their timeline, let it play, start/stop, reposition the cursor, and watch the graph.