Problem when using gtid with MySQL replication
I've been having this issue on a new install of 5.6.26. I found a bug report on this and it suggests that the fix is available on 5.6.27 or 5.7.9.

https://bugs.mysql.com/bug.php?id=68525

I've upgraded to 5.6.27 and just watching to see if it happens again.

Hope this helps.