To downgrade, you can try to find the apk files from another source such as apkpure (but beware of the risk of installing app from outside Google Playstore), I suggeat version 4.10 because the sync functionality is still working, rather than version 4.11.
But if you have patience (Ecclesiaste 10:4b), you can wait the developers fix the problem, and meanwhile you can backup you Bookmarks, Notes, and Highlights with the In-app feature "Data Transfer" in Setting section. Good luck GB.