Hi there and welcome
Can you please do the following in Safari
Click Safari, Preferences, then Advance
Click the Show Develop menu in menu bar optionSelect Empty Caches from this menu
Once done, close Safari, open it and try to open Audible
I can also do these steps for you, and have made a request via Additional Services. This is optional, and if you choose to do this, I can, with your permission, remote into your computer while you watch and do all these steps (and deal with any problems that arise during them) for you. Or if you do not choose to take this service, we can continue here. This is no problem at all. Just let me know please.
Else let me know please the results