Onslaught on kill Jewel And Radiant Crusade Ascendancy

I have an onslaught on kill jewel equipped and this does not seem to be working nicely with the Radiant Crusade ascendancy. I had 1 golem and the onslaugh buff seems to stay active for a second before disappearing.

In my understanding i should be able to have both the 10% more dmg buff and the onslaught buff active at the same time