Stable Aspect doesn't seem to activate Unstable Currents

I’m running an orbiting lightning ball build. I’m using the ‘hold’ feature for skills. The lightning ball skill is casting about 5 or more times a second, fast enough that I often have a solid line of lightning balls orbiting. Now, I have the Stable Aspect aspect on my weapon, and it appears that Unstable Currents never autoactivates. The only time I see Unstable Currents is when I manually activate it.
My Stable Aspect indicates a 16.5% chance to activate with casting lightning spells. I’m most likely casting Lightning Ball at least 60 to 100 times a minute. According to that frequency I should be seeing an autocast of Unstable Currents at least 1 time per minute. What’s up?

The Stable aspect doesn’t cast Unstable Currents.

It simply triggers a free cast of Shock spell when Unstable Currents is not active. It’s a very underwhelming aspect.