Hey, I just noticed this as an issue yesterday. I just got it working again.
I guess Evernote for web just got a redesign or something (the sidebar is black). I clicked on my name in the top-left corner and there was a button in the menu that says "Switch to older version of Evernote".
Once I switched back, it started working again.
For anyone coming across this post and wondering what the deal is, there are regular note links (starting with https://www.evernote.com/shard/...) and classic note links (evernote:///view/...). I have a Mac at home and I use the Evernote app. I use Todoist and put note links in Todoist sometimes. I can use the classic note link which will open right to Evernote in the app. However, on my work PC, I'm not permitted to download Evernote, so I prefer to use the http links. On my home machine, the http links opened a browser tab, then immediately opens the note in-app. Something about the redesign changed that.