Using the deep link in OneNote app or OneNote 2016 opens Teams but does not start a chat with the user you included in the link.

Using deep link: msteams:/l/chat/0/0?users=someone@somewhere.com

If I paste that into a web browser it will open Teams and start a chat with someone@somewhere.com. If I create a hyperlink with that in OneNote, it will open Teams but not create a chat with the user.

I noticed in the warning popup window in OneNote 2016 that it's warning me about url:
msteams://l/chat/0/0?users=someone@somewhere.com (note the double-slash after msteams: instead of a single slash)

That's when I noticed OneNote was "correcting" my URL to have double-slashes. It would not keep my single-slash no matter how many times I changed it.

I then pasted that double-slash version into a web browser and it did the same thing - opened Teams but did not create a chat with the user.

Not sure if the problem is that OneNote (presumably any Office app) is tacking on the extra slash or that Teams doesn't know what to do with it.