Hi @lenz ...
I see that you received a response from @AngelaBBurgess this weekend (thanks Angela!) located at Re: Canvas Inbox (Conversations) Error for just me... - Instructure Community - 627686. I would also encourage you to reach out to the Canvas Help Desk staff about the issue you are experiencing with the Canvas Inbox. Canvas Tech Support can attach your issue to the existing trouble ticket...so that when it has been fixed/resolved, you would be updated about it.
Also, I wanted to let you know that I went to the Known Issues - Instructure Community page here in the Community, and I filtered for "Canvas Inbox", but I did not see anything listed. I'm not certain on this (since I don't work for Instructure), but the issue may be too new yet, and that's why there isn't anything I can find on this page related to the issue.
I hope this will be of some help to you.