I've been encountering this a lot as well. It only seems to happen on the first load though, a simple F5 or if I've viewed it recently it'll be fine. This is such a huge aesthetic issue I'm wondering why it still seems to persist, or if there's some kind of workaround to get it to size correctly the first time.
I'm close to trialing a jank workaround where I find somewhere to host an HTML file which is just a dashboard imbedded with nothing else and does a refresh a second after the page loads the first time.