Like many in the past, my team had severe trouble completing weave 12, as the end sequence would crash over and over again after the first wave of bomber rats. We must have crashed nearly a dozen times before we came across a solution, thought I’d share that solution here to help out my brethren.
If you’re having the problem (game crashing after the first wave of rats/when the gunners show up), have everyone in your party do a complete reset of your Xboxs. If you’re not familiar on how to do this, have everyone in your party hold the xbox power button (on the console) down for 10 seconds. Hold the button until you hear the turn-off noise, then restart the console. You should see the green Xbox One starter screen if you do this correctly.
We also had the one person on a Xbox One X host the session after the complete reset. Not sure if this helps at all (they hosted before the reset and we still crashed) but worth doing in addition just in case.
You know it works when you notice the sequence of waves in the final round differing (aka the exploding rats and gunners come at different times).
Wish someone had told me about this, as it would have saved me hours of aggravation.