In the last updates, some changes indeed happen to the Account Manager (uptate 1.5).
It is then possible that some changes in the configuration of the Account manager to the new DAVx5 version imply the current behaviour of our app (Account manager Git project, DAVx5 Git project).
So as it seems to be that the DAVx5 update raised no issue on this topic, may be downloading the app in the app Lounge is maybe one temporary solution to get your e account back on your phone (I am not sure). Then we can hope that next update 1.6. will solve the issue (as we can see on the git, the project edition is still active and the modification will probably be introduced with a newer version).
I am sorry, I am not very helpful, but I am also a bit lost about what can be the source of the issue 