This has been a constant issue that I and other players face, it felt like I had to slam on buttons to change or even use skills, and literally couldn't even switch to my back bar to heal, buff etc, let alone how did I die in a different location?
Happened to me a thousand times, you almost die, want to switch to the other bar with heal/shield.
Bar swap doesnt work so you press it again, finally swaps bars, swaps bars again before you can cast the heal/shield.