Nicknames of your characters. Lefap
Information about your Game Client. 5.4.8, downloaded from your site
Describe your problem. I keep on killing this timeless isle rare mob and it doesn't get counted for the achievement (as you can see I have killed the rest of those)
How you tried to solve the problem. Tried killing him several times
Screenshots with problem. http://prntscr.com/9xr3w5 - me after killing him, loot table is seen and him as my target
http://prntscr.com/9xr42l - achievement's screenshot, you can see that every other rare was killed and it counted, but not this one.
I also know that I'm not the only one who experienced this bug.