On some Android 4.1 devices or on some Samsung Galaxy S4 – if you install DAVdroid, set up an account and restart your device afterwards the account will be missing.
Account vanishing/missing after device restart
This behaviour is an Android specific bug and does not rely on the app side. Android is deleting DRM secured apps (paid through Google Play) after a restart on these versions / devices because it checks accounts and apps in wrong order.
Important notice: This is NOT happening on apps that you got via F-Droid.