This spell, magicka regeneration wise, has always been pretty horrible. You see folks posting like it is our regen tool, which is silly given that without reduction stacking it does not even cover the cost of casting the spell, and even with all of my reduction stacking at V12 I only gain 40 magicka if I stand in the circle the entire 15 seconds, which lets face it... not that practical in a lot of situations.
That said before the patch it worked. The patch notes said:
Channeled Focus: Fixed an issue where Channeled Focus was not giving the intended amount of magicka.
I am not sure what the 'issue' was before, seemed to work fine for me, but now I am not getting even half as much as I should be. It seems random if you will get the .5 second tick or not, the most I have gotten is 14 out of a total of 30 possible ticks, meaning it is less than half as effective as what it was. I will get a bunch, then miss some, then get some more, or I will get nothing and then the last two.
In the big scheme of issues, this is not really that big of a deal given it sucks horribly even if it was working, but as something that was supposed to be 'fixed' it is now entirely broken.