On the server is no player with nickname "Boat"

I see in the console:

[15:05:02] [Server thread/INFO]: Saving...
[15:05:02] [Server thread/INFO]: Saved the world
[15:08:00] [Server thread/WARN]: Boat moved wrongly!
[15:08:01] [Server thread/WARN]: Boat moved wrongly!
[15:08:01] [Server thread/WARN]: Boat moved wrongly!
[15:08:01] [Server thread/WARN]: Boat moved wrongly!
[15:08:01] [Server thread/WARN]: Boat moved wrongly!
[15:08:01] [Server thread/WARN]: Boat moved wrongly!
[15:08:01] [Server thread/WARN]: Boat moved wrongly!
[15:08:01] [Server thread/WARN]: Boat moved wrongly!
[15:08:02] [Server thread/WARN]: Boat moved wrongly!
[15:08:02] [Server thread/WARN]: Boat moved wrongly!
save-all
[15:10:01] [Server thread/INFO]: Saving...
[15:10:01] [Server thread/INFO]: Saved the world
list
[15:12:38] [Server thread/INFO]: There are 3/16 players online:
[15:12:38] [Server thread/INFO]: Fairas2013, Smasherfl, Jeabit