This happened in a not too recent patch where some VFX were removed despite being of the lowest quality possible: Golden circular wave that appears and spreads out when an arena ambush event occurs.
But in the latest update, a Mob Flair named Vanish doesn't contain all the visual effects that his icon promises.
UPDATED:
Apparently he didn't understand me, at least in the example of the golden circle that extends in the arena events. Here I leave a more explicit example to support my report.
The main case of the report is the mob flair that does not contain the VFX that its icon promises, which I suppose you have checked and succeeded in finding.