I've never even seen a cinnamon roast offered. Maybe your roaster could give you some advise on dose? I'd guess you would want to updose quite a bit because the coffee itself is much more dense requiring more grinds to filll the basket. Maybe try the coin trick to gauge the distance between the puck and the screen?

First thing to look is your equipment, when was the last time you cleanup your grinder and how old are your burrs. Secondly, as Tom mentioned, verry light roast can be hard to work with, you can try a roast from one of the site sponser that is well known to compare with of your local roaster.
Underdeveloped roast is also a problem with roaster trying to go "light" these days.
You can also distribute the grind in a second vessel and shake it before distribution in your pf. Worked for me in the past with a super Joly.

Hi Josiah - in my experience, channeling is merely a distribution issue. I would use some form of palm tapping to settle and distribute the grounds. Using your fingers to move the coffee around or smooth out the top doesn't effectively address potential cavities below the top. Tapping uses gravity to help with this.

If your shots are simply running too fast, increasing your dose will help slow them down a bit but won't necessarily get better flavor. I'm not sure what ratio you're aiming for, but with lighter roasted bright coffees I aim for a longer shot. (Ex: 18g dose, 40-45g yield). Since lighter roasts leave the beans less broken down they are harder for grinders to break up. If your shots are screaming out in under ten seconds and you can't grind any finer, that does sound like a grinder issue. Good luck!