Try using a hammer (I did it with the Iron Hammer) and then go to this site,
http://www.metronomeonline.com/
Change the the clicking speed to 92 and press X to swing every time it clicks. You don't have to be attacking anybody you just need to be doing it within a certain Rhythm so try and find an area that has a lot of space.
You'll know you've done a chain attack when you swing your sword and a blue animation shows the swipe. To avoid confusion use a weapon with no augmentations assigned as they can make your weapon give of a colour as well. Remember that you have to tap X and then tap it again at the peak of the the swing to perform a chain attack. Be sure to do it in Rhythm.
Regardless as to how convinced you may be, you probably haven't done it yet. Video games are programmed alike a machine is. You wouldn't expect a working toaster to forget about toasting your bread. And the achievement definitely hasn't glitched or broken in any way because it worked for me just fine before I downloaded the patched update a long while ago and it still works now (I recently got all achievements completed on a new GT).
Good luck getting the Achievement, I know they can be a pain in the rear end to unlock at times. B)