I know the countdown timer and how it shortens during use, for Nova necs with bone shield.
For the last month or so when using it, I carefully watch for the CD timer, and then the duration timers as they shrink with use. However in boss or even trash fights, I have seen, about 20% of the time, my nec getting a full 10 stack bone shield, and then the CD timer doesnt go off, I see the countdown timer flash, and the 10 stack is instantly gone. This is obviously not in line with the mechanic, so its a bug. And 65s ping, so its not lag.
Or in other cases, I get the CD timer normally, and the countdown timer flashes and its insta-gone even though I back off nova to make sure the timer doesnt go too fast. This happens especially with end GR bosses, most notably the Herald of Pestilence boss.