Hey did you fixes your inbox problem? The same happen to me, my inbox for DM vanished and only shows my "activity" in the middle. So how did you fix it?
Already answered in inbox. But in case anyone else having the same problem. What you should do is.
1. Open tumblr on your laptop then click setting.
2. Scroll down until you see Help function click on it.
3. Then scroll down again until you see contact support, click on it.
4. There's so many option to what kind of problem you're experiencing, choose one of it that's close to yours and then provide screenshot and also explain a little on the box to the staff about your problem.
5. Don't forget to choose which blog experiencing this problem if you haven many side account or something.
6. Wait for their reply to your email, you can communicate with them through email like if it takes them longer than 3 days, message them again asking for follow up, If they didn't reply, re sending the complaint all over again.