I’ve recreated this issue 6-7 times now, and it happens with and without any addons.
During the Emberflow Flight Race the last 4-5 rings will despawn every single time. The race then fails due to missing rings that can’t be seen.
Here is a video showing it happening =
Same issue here. I believe it’s related to phasing at the Obsidian Citadel. Please fix this Blizz it’s the last advanced gold race I need 
I have the same issue.
Not only do the rings disappear, but after 1/2 dozen or so tries I twice was dismounted. I completed this on another toon, but I assume it was because I had not advanced to the Obsidian Citadel quests yet.