I have recently tried builds both with and without Explosive Shot and Dire Beast (exclusive to each other).
In both cases, either ES or DB is the last ability shown on the right in the cooldown bar in Edit Mode.
However, the ability is usually not actually shown in combat in delves or open world (all I’ve tried). It occasionally shows up on the target dummy, but I haven’t been able to figure out the trigger (Maybe right after I’ve moved the bar in Edit Options? Not sure.)
The spot is just left blank and the CD Manager doesn’t show the icons. I have my CD Manager bar set to only show in combat. This issue does not seem to occur when the CD bar is always visible.
ETA: I have found also happens in some cases when I have the cooldown manager always visible. Again only seeing it on my hunter. It happens when I zone into an instance, and the workaround is to go to the Edit Options screen, which causes the full cooldown manager bar to become visible.
Additionally, I have also had the left-most ability (Cobra Shot) to sometimes be missing as well.