For starters, I apologize in advance for necro'ing this thread. I wouldn't do so unless the OP was unanswered, and I had the answer.
I ran into this same issue, and everywhere I went I saw the same answer, that being "You aren't killing enemies fast enough", which certainly wasn't the case for me, so I doubted it was the case for others either.
After playing around in the simulacra, I figured out the misunderstanding. Cathode Grace has a duration of 8s, a cooldown of 60s at base, and awards +3s per kill. The duration, and duration per kill is affected by power duration, but the cooldown timer is not.
When you use the ability, you will notice in the bottom right corner that it is active, with a timer on it that is counting down. Once the timer hits 0, it will 'reset' to 59, and there will be a small white pi chart above the numbers indicating that this is now your cooldown timer. While Cathode Grace is on cooldown, it is not active, and therefore will not accrue bonus time for itself or Rotorswell (w/ Cathode Current installed ofc).
Personally? This issue was rather bothersome to figure out. I am not aware offhand of any other Warframe ability which has an inactive cooldown (even if there are, I'm positive none are anywhere near this punishing). What's more, the only thing which distinguishes your 'active' timer from your 'cooldown' timer is a tiny little pi chart which most players would never even see, much less understand the meaning behind it. If I were making any recommendations to DE on the matter, I would suggest changing the text on the cooldown timer to be red to make it especially clear that the ability is not active, and is on cooldown.
Overall, Cathode Current isn't restoring your Cathode Grace or Rotorswell timers because Cathode Grace isn't active - it is on cooldown. Wait out the timer, re-cast, and start killing ASAP to get your snowball going again.
Good hunting, Tenno.