I had this problem on my iPhone a few months ago, and then I noticed I didn't, because... no freakin' clue.

In the "have you tried turning it off and back on again" school of troubleshooting, try deleting the Medium app from your phone and then reinstalling it. If that doesn't work the first time, do it again, but this time turn around three times while holding your left ear with your right hand and gargling salt water. ¯\_ (ツ)_/¯