[schapplm]

So the addon seems to work in principal:

06:43:03.527 T:139774566573824  NOTICE: service.watchedlist: Notification. WatchedList: 31 movies and 187 episodes read from WL.
06:43:03.860 T:139774566573824  NOTICE: service.watchedlist: Notification. WatchedList: 220 movies and 2286 episodes read from Kodi-DB.

What makes me wonder is the format of your addon settings. Yours is the template file coming with the addon.
The settings.xml should look like this:

xml:
<settings>

    <setting id="autostart" value="false" />

    <setting id="db_format" value="0" />

    <setting id="dbbackup" value="true" />

    <setting id="dbbackupcount" value="4" />

   ....

</settings>

db_format is the option for SQLite file or mySQL.
It seems like your settings are somehow not set and you use the default watchedlist.db file instead of your mysql database.
I think you mixed up ~/.kodi/userdata/addon_data/service.watchedlist/settings.xml with ~/.kodi/addons/service.watchedlist/resources/settings.xml.

Or do you have a platform where the directory structure is somehow different?