The Radiant buff you get when you leave Well of Radiance is not giving weapons Anti Barrier Rounds. I was using Radiant to cover that type of champion for nightfalls, the buff obtained from using my melee as a solar warlock was correctly applying Anti-Barrier Rounds to my Xenophage, near the end of the strike I had a Barrier Centurion to kill, but didn't have a melee charge, so I used well to get Radiant that way, however as shown in the screenshot, the buff obtained that way doesn't grant my Xenophage Anti-Barrier rounds