We are running a newer version of Discourse here than we were at happymutants.space. That may be the difference, but not the underlying cause.
Which theme are you using? Does changing it have any effect?
Have you tried the Discourse App? I’d be interested to see if you are getting different results.
All of the buttons are decorated using glyphs from Font Awesome, so it may also be worth checking out if you want to investigate further. I believe we’re using 4.7.0 here, but it looks like it’s the same version at the old location as well. In both cases, they are hosted internally instead of a CDN, so I don’t imagine that to be an issue.
I’ll look into this a bit later and see if there’s any other troubleshooting I can do. I don’t have an iOS device, so I’ll have to rely on you and others to report back.