This issue did not happen to my minecraft, but to my firends one, so:
When my friend tried to join his private minecraft server (this happens nearly every time he joins), The chat is filled with
"KarateKarotte joined the game,
KarateKarotte left the game,
KarateKarotte left the game,
KarateKarotte left the game,
KarateKarotte joined the game"
in a random order. Actually he is never on the server (you can't see him using tab).
In the Attachment you can see the user created crash report and the server.log file
[There coud be some other failures in the crash file, because of a power failure, but this also happend much earlier]
Attachments
Comments 3
-There is some corruption going on on the server, see MC-2545 for that to fix the corrupted chunks.
-Your Java version is outdated on the server (hightly outdated, the one you are using has some security issues
-The issue potentially relates to "Failed to verify username!", which was an issue about 1 1/2 years ago. Please do the steps above to see if it still happens, and we will come back to you.
Also after rejoining the server it works just fine.