We had this problem reported and are posting the conclusion in case other people have the same problem.
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"I have been having issues with the 3d mark tests, most noticeably the DX11 test. As you know, the test normally starts scrolling across an empty plain until it reaches the base and scrolls up to view the space jellyfish. However, when I run my tests lately the test shows a black screen for a few seconds and when it finally loads in it is already at the space base and beginning to pan to the right looking at the jellyfish."
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This happened on a GTX 1070 card on multiple different versions of windows. The effect on the benchmark was to lower the average frame rate for the DX11 test as the start of the test records 0 fps.

The cause was found to the Geforce Experience software's 'Share' feature. Turning this off removed the lag and improved the frame rate.