Medium is using 302 redirects on most pages coupled with 301 ones as well at some places. I counted two 302 and one 301 on the link you posted from the sitemap. Even the homepage goes through two 302 ones. That’s too many for few simple links. No wonder Google takes times and faces problems in indexing them properly. Eventually it should be able to index though. The homepage seems to have gotten indexed this time but description got blocked. Maybe redirects I guess? Talk to them.