Having the exact same issue.
I'll just sit there for a good minute (sometimes longer), using shout or flight in attempts to regain rage, but it doesn't budge. Doesn't regen passively either... Surprise surprise more build-breaking bugs.

I am having the same problem when i switched to a rage build, at higher levels it straight up killed me because i suddenly I am not able to do anything because Willpower and Rage are glitching out to the point that i cant cast or use any of my abilities at all. Happen to me on a level 128 expedition boss and i lost because i could not use my movement spell and got smashed.i raged quit!! I love this game but i hate that i feel like learning how to combat all the bugs as well as a optmizing your build are just as important. Really hope they focus on bug fixing this next patch instead of balancing/nurfing. Lets make sure the game works before making everybody have to re learn what is actually good again when you change all the skill, modifers and nodes.

Side note: Im really patient with this game becuase i play alot fallout and skyrim. When everything is working i love this game, but when its not its terrible and the bad kind of frustrating.