I happened to have my phone sideways when I cast a close vote and noticed that half the close reasons are of a different text size. This is not the case in portrait mode. Reproduced for testing on both SO and Server Fault so presumably it’s network-wide.
Similar inconsistencies show up in the community specific reasons as well:
(Click through to see full-size pictures.)
This is on an iPhone 11 Pro; I hooked up my phone to my MacBook to use Safari's remote DOM inspector. The HTML and CSS for both items appears identical, including the
font-family: -apple-system,BlinkMacSystemFont,"Segoe UI Adjusted","Segoe UI","Liberation Sans",sans-serif;
But for some reason, checking the font tab shows the regular sized text is rendering in ".AppleSystemUIFont" while the large text uses ".SF UI".