It's been an issue since release. The PC devs are testing a fix but they say it is a very hard bug to fix. 

I believe one way to help against it, if your playing in fullscreen, is to pause, alt tab out, go do what ever you needed to do, alt tab back in, then un pause.

So right now i pretty much can't pause a solo game of zombies or i'll die as soon as i unpause it. I get the connection interrupted message and i can't move but the zombies can. A little googling and i've found that this issues has been going on for some pc players since launch. The only fix suggested is pausing and unpausing with a controller. 3arc please look into this.

[PC] unpausing a solo game of zombies gives me a connection interrupted.