As you can see in the video linked below, resizing modals in Cornerstone is anything but smooth. It’s very choppy, like playing a game with low frame rates 
Video: https://www.dropbox.com/s/cgsc8zdqj255fwk/screencast-cs-modal-resizing.mp4?dl=0 Check the last couple of seconds where I’m resizing the modal more aggressively.
FWIW I’m on a Windows 10 machine and I’ve tested it in Opera and Firefox.
@JvP, we will keep an eye on this, but this could be related to a multitude of factors on your machine. I do not currently experience any sort of choppiness when resizing the modals on my very old machine that is on it’s last leg. I am also usually running dozens of apps, build scripts, code editors, browsers, et cetera all at once and I have never seen this type of behavior. It could be a process happening locally on your machine that is chewing into your processing. I have tested this in Edge, Opera, Safari, Brave, Chrome, and Firefox on my machine and they are all remaining smooth at this time even with all of my processes running and on a very old machine.
Ok, must be me then. I’m using a self built PC from around 2012 so not exactly the latest hardware either, haha. Still going strong though. Resizing OS windows is buttery smooth though so it must be something browser related.
I hear you…my machine isn’t quite there, but it’s a 2015 and very much ready for retirement after all I’ve put it through, ha. I will certainly keep an eye on it, I just can’t replicate that exactly, and you’d think I would be able to with all of the stuff I have running in the background constantly keeping this dev environment up.
Yeah and nobody else seems to experience it either. I’ll just live with it 
We will keep an eye on it as mentioned above.