This bug was discovered by my group on the 29th of August, and I do not have video proof, but this happened to my guild again on the 3rd of September.
If the Yokeda Rok'dun group all dies, the boss will not respawn, and the only fix is for the group to Reset the Instance entirely, and start over.
This is progress blocking, because newer players cannot learn a fight, if they have to restart the trial over and over and over to learn the Yokeda Rok'dun fight.
(Video shows what we tried, we all tried dying, killing extra mobs, ect, and nothing worked. Shows the fight, and our group dying to mechanics, and shows that Yokeda Rok'dun is nowhere to be seen.)
I submitted an In-Game bug with Reference Number: 190903-004990 last night, but this is video proof of the bug happening on the 29th of August.