Had this happen 3 times today so thought I would report it.
When I come back from a map (nords and black knights) my book maker says that my book is ready to pick up, I can even pick up the book and make a new book.
The little book complete symbol shows above my barracks and my book maker.
I get lots of notifications (like 20+) that my troops are ready.
When I refresh the game the book making goes back to what ever time it was on before. No idea if it takes the resources to make a new book as I didn't check how many resources I had before I made a new book. I made a new book as I thought the book was ready to be picked up, however I did not get the book.
Nothing major but thought you might like to know.