Focus randomly being lost

I have been having an issue with Minecraft for about 6 months. Every time I play for any extended length of time, my Minecraft will lose focus, causing my character to keep walking for a moment as the Menu opens up. From what I can tell, this issue occurs completely randomly (No screen re-siving or lack there of changes it's likeliness to happen), and it has made Minecraft completely unplayable in Survival mode. I can Manage in Creative, but I miss playing with my friends.