It's no longer speculation. It's official. Hurdle 5 in Sydney McLaughlin's 51.61 race today was placed about 5 meters too far away from hurdle 4. (Meaning that it was also about 5 meters too close to hurdle 6.)
Whoever set up the hurdles accidentally placed the 5th hurdles on the yellow triangle, which is the beginning of the passing zone for the 4x100. The yellow triangle has nothing to do with a women's 400H race.
About 5 meters before the yellow triangles, there is a small mark on the track (which is too small to be seen on the video) which is where the 5th hurdle for the women's' 400H should be placed.
So here is what most of the women in the race ended up doing:
15 steps - hurdle 3 to hurdle 4
17 steps - hurdle 4 to hurdle 5
13 steps - hurdle 5 to hurdle 6
15 steps - hurdle 6 to hurdle 7
Between hurdles 5 and 6, Sydney McLaughlin actually had to chop her steps to run 13 steps. If she hadn't chopped her steps, then she would have run only 12 steps, which is impossible for a women to do.
The hurdle placement error makes McLaughlin 51.61 even more impressive.
The crazy thing is that if McLaughlin hadn't chopped her steps on hurdle 9 and 10 (which were placed correctly) then she would have broken the world record.
Would that world record have counted? I don't know. She still would have run 400 meters and cleared 10 hurdles, and the mistake on the placement of hurdle 5 actually made her race more difficult, not easier.