Interestingly enough I have that very same issue, but only on one of my toons.
It is not lag, it is not server re-set related. The buff literally disappears as soon as you get it, long before the announcement is made for the next rune. I tried re-logging, changing classes, removing all buffs, changing gear, changing channels, dropping/re-taking quest...all the standard stuff. It is not even a difficult challenge, of the 6 toons I ran through 4 did it first try, 1 took 3 attampts, which was probably overconfidence on my part. But this one toon, well, basically he just gave up on that quest.