The error in the log does not lead to the debugger crashing. The renderer sandbox is an optional protective feature for the web rendering code. The error is logged by CEF (the framework we're using in the DevTools window) and it can be ignored.
As for the debugger crashing, I am afraid that something in your code is causing the app to crash. I suppose at that time, the debugger is closed as it cannot run when the app dies. Unfortunately I am not aware of a good approach that would allow you to easily get the stack trace of the error from the device while you're working in a Windows environment.
The device logs would hold the exact cause for the error - usually when the app crashes, the root cause lies somewhere in the native code and the AppBuilder DevTools
cannot get that exception as they close with the app. You can get the device logs on a Windows
machine once you sync your device through iTunes - this article
describes that option in more details. However, since Apple symbolicates the iPhones crash reports, outside xCode it's hard to get to the stack trace of the error.
You can try narrowing down the piece of code leading to the crash by removing parts of it until you get to the exact line that crashes the app. As long as your app is running, the AppBuilder DevTools
should also run and you should be able to debug the app - hopefully you will be able to get down to the exact error that way.