I've just run across this myself, I think. It's certainly a selector bug that makes things vanish. For me, it's the selector \FE0E to force a text presentation (monochrome) of an emoji character. For the icon font I made, I chose to use symbols that already had meanings that matched the icons I was creating. This was not only done with fallbacks in mind, but for accessibility. For example, on every other OS and platform, \1F6D2\FE0E renders my monochrome symbol for a shopping cart. This works even on webkit compiled for Linux and Windows, and even on Safari in MacOS. I tried it out on browserstack and the vanishing bug seems to have popped up as far back as 17.2.1, it's certainly not there for 17.1 or iOS versions before 17. And the bug is still there for 17.3.1. I wonder if there are any CSS Selector hacks to identify iOS17+. I hate to add UA sniffing JS just for this bug. Hopefully it's short lived.