it’s neither a server nor a problem with DAVdroid. The error comes from the Android base system. Some users already reported the problem, but we couldn’t reproduce it on our own. All we know is that it only occurs on some Android 8.0.0 builds. Most of the time when the manufacturer updates the devices to a certain build of Andorid 8.0.
The good thing is, many users also report that the error simply vanishes after some time. Either by un- and re-installing DAVdroid some times or when the manufacturer updates the device again.
We think that it oly occurs on very special builds of 8.0.0 and it is maybe related to a caching problem of these Android builds.
This is a duplicate of: https://forums.bitfire.at/post/9654