This is kinda similar to what someone posted about vital area, but about overhead. So to begin with, even at 100% it was unreliable and missed quite often, fine. I then decided to try the Axe murderer edge and was pleasently surprised, as it made this rather niche skill reliable so that it almost never missed (in addition to what is described in the help file).

But recently it started again failing a lot, it FEELS like it misses even more than before the edge. Throughout all this the eq used has been basically the same nor has anything else has changed.

Nothing has changed.
Seems to be landing sometimes and not others (it's not the most accurate skill).
Works fine, so no bug in sight.