Swift: App crashing during segue

I have 3 view controllers that I'm navigating between. When I open my app, I start at Controller1, which I can then use to navigate to Controller2 or Controller3. I can navigate to each of them fine individually, however, after I go to Controller3, return to Controller1, then try to navigate to Controller2, I get an EXC_BAD_ACCESS with code = 1. There is no exception or error message given at all, it just takes me to my AppDelegate file and gives me that error code.

I don't know what the issue is, but something that seems relevant is that I'm setting Controller3 as the navigation controller's delegate. I have a fourth navigation controller that also is set as a delegate as well, and causes the same behavior when I from 1->4->1->2, just like with 1->3->1->2. I have no issue going from 1->4->1->3 or 1->3->1->4, only when 2 is involved. I'm not sure if the issue is the delegates, and the fact that 2 isn't being set as one. Once again, I can navigate to it fine by itself, but not after navigating to one of the other 2 sub-view controllers.