I’m using Paratext on Linux, and here’s a screenshot of the project.
I noticed that my colleague using Windows has the same problem in the project, except with his message there are three links: one to restore the deleted book, one to create the book and one to import a book. Clicking the restore option on his computer didn’t help the situation (again a dialog asking if we want to add the book to the project for tracking, then nothing)
I was able to resolve the problem by going into recent changes for the project and undoing the change that deleted the book.