2017-10-22, 10:55 PM
Finally, I solved it with database synchronization 
Little clue:
This unfortunate misfortune would not have happened if my admin-cp had been set to English.
When uninstalling the plugin, it says something like,"would you like to drop the entries from database?" That's a clear message.
The German version only says: "Do you want to uninstall the plugin".
I have two/three other problems.
1. In the plugin settings I have several fields which are not occupied or labeled, see screenshots.
2. Although it seems to be set, I don't get any JGrowl notifications, see also screenshot.
3. What value can be set at the bottom?
best regards

Little clue:
This unfortunate misfortune would not have happened if my admin-cp had been set to English.
When uninstalling the plugin, it says something like,"would you like to drop the entries from database?" That's a clear message.
The German version only says: "Do you want to uninstall the plugin".

I have two/three other problems.
1. In the plugin settings I have several fields which are not occupied or labeled, see screenshots.
2. Although it seems to be set, I don't get any JGrowl notifications, see also screenshot.
3. What value can be set at the bottom?
best regards