I have tried this as well.
I'm experiencing the same thing on my Samsung Galaxy S10+ - no books are syncing regardless of my attempts to uninstall, deregister/deauthorise, toggle between sync or not. I have however discovered that 2-factor authentication must be disabled to use ADE.
And I have the same issue too. Frustrating. Especially because Adobe won't even address the issue on their chat support service. Just sends you over here... Where there are no answers apparently.
Does anybody have a solution?
Sorry to hear you have the same problem. I did not find any solution too and adobe did not offer any answers. I am currently using overdrive instead and have no problem with that!