Clicking the above button brings up a MUI dialog which contains a simple header, 10 MUI text fields, and 10 interleaved divs. In Safari, if you make the height of the browser window short enough, you should see that the header and the 10 interleaved divs will either disappear completely, or will be cut off. I'm running Mojave 10.14.2, and Safari 12.0.2 (14606.3.4), running no extensions.

Full disclosure: one other developer saw the same issue I did, and another developer did not. We could not account for the difference. We are all running macOS, with Mojave 10.14.2 and Safari 12.0.2. Also, FWIW, Safari won't load this Codesandbox maybe 75% of the time. When it finally does load, it "works" in that it shows the error, but for whatever reason, Safari chokes.