Not saying this happened to you, but I once lost half an hour to figuring out wth I lost all my Audible books when getting a new device (phone). Turned out the app happily logged me in to audible UK without saying anything (silently creating a new account), which, of course was empty.
Once I figured out how to point the app to Audible US, all my content was back.
Once I figured out how to point the app to Audible US, all my content was back.