How to capture a log
In Android 4.1 new security restrictions have been introduced. As a result it has become impossible to record a system log (using apps like CatLog) without having rooted the device. Since most apps write their debug information to the system log it has become harder for developers to get the information they need to resolve issues.
To address this limitation newer releases of CalDAV-Sync, CardDAV-Sync and SmoothSync have a new option to log their debug info to a file. To enable this feature start the app, enter "Debug options" and enable "Log to file". This feature is disabled by default because writing an additional log file causes additional overhead and you should disable it again once the issue has been resolved.
When the option is enabled the app will preserve up to three log files (of the three most recent syncs). You can see the log file in the "Debug options" menu by tapping on their name. To send the log, just open a log, tap the send button and send them to email@example.com via e-mail.
If you have root access, you can as well access the logs at /data/data/org.dmfs.caldav.lib/files/