Jank can be caused by background network activity,
I think the web worker thing was supposed to solve this by having the game on a separate thread
but (dont quote me on this as I'm not as up to date on construct news I used to be)
but the last I read on one of Ashley's updates was that the worker thing was deactivated for now pending a future update of chrome . that was a couple of months back I think so not sure if there has been an update since then.
You can enable web worker in the settings, with enable experimental features checked, this is in the latest stable r131.
There is no less visible scrolling jank difference, with my laptop, with this enabled.
I am not knocking c3, in fact I think it's great, and will re-subscribe, but we are limited to chrome, or chrome variants, so it does matter, it affects what we produce, for our target markets, most issues are normally fixed by advances in technology, but this one seems to be hanging around.