deusgog
I updated to 1.2.3.8 and kept getting auth failed issues. I couldn’t even change the path to kindle in settings. After messing around with everything for a bit. I deleted all downloaded books, uninstalled both kindle and bookfab. Did a clean install of both. Started up kindle, downloaded some books, started up bookfab and it worked for the most part. However for some reason half the books were showing as their random letter/numbers. They still decrypted but did not title properly. Luckily calibre was still able to recognize them.
Worse comes to worse, you can try clean wipe of books, data and apps, then do a clean reinstall to see if that works for you.