[schapplm]

Error: Writing the WL-database file (2055: Lost connection to MySQL server at 'host:3306', system error: 104 Connection reset by peer)."

I can only guess that the addon is running so long that the initial connection to the database is not valid any more due to a reset.
In the python code, first the mySQL connection is established, then the databases are parsed and then changes are written.
This is very hard to debug, though, since it seems run-time dependent and also dependent on the individual client-server and network configuration.
If this only occurs sometimes, better to just ignore it, since it does not disturb the overall result of the addon. The databases are synchronized just later.
When running the synchronization in background, this should not be an issue.