Although it has grown to become an excellent Gmail alternative, Google's Inbox app remains an experimental piece of code. This means that Google is using the data provided by its usage to improve Gmail and, unfortunately, it seems that the internet giant has decided to discontinue Inbox at the end of March 2019.
https://www.notebookcheck.net/Google-plans-to-shut-down-the-Inbox-app-by-March-2019.331472.0.html
I think they should totally kill Gmail and move to Inbox full-time. It's the future. It's simpler, better designed, and just something different than the typical email inbox.
Google should really keep Inbox. So much smoother, simpler and less clutter.
There should be a coordinated effort to let Google know what a mistake they are making!
I wouldn't know where but perhaps you do.