I wouldn’t know for sure whether this has something to do with OS or not. The same thing happens to me on my Android, though, but not on my laptop. I do not use Medium mobile app, I use browser to access it but the experience and homepage are nevertheless not the same as on laptop.

Medium, however, has had many issues with mobile devices so far, so if your using a mobile device, this might be reason. Or, it could have to do with one of their ‘upgrades.’ They are constantly experimenting with those too. Maybe it would be best to ask their customer service, they should know why this is happening.