This is a pretty strange one. I've spent a few hours tracking it down to the source and I have it to a point where it crashes 100% of the time.
The command format["%1n", _undefVar] (where _undefVar is undefined) in scheduled space only will cause a Windows invoked "Arma3.exe has stopped responding". Global and local variables will both present the crash.
-showScriptErrors must be enabled.

format["%1next", _next] will crash, if _next is undefined.
format["%1n", ] will crash -just by being compiled-!

format["%1n", nil] will -not- crash, showing no errors.
format["%1", _next] will -not- crash, showing undefined var script error.
format["%1v", _next] will -not- crash, showing undefined var error.
format["%1v",, ] will -not- crash, showing invalid number in expression.
format["n%1", _undefVar] will -not- crash, showing undefined var.
format["n%1", ] will -not- crash, showing missing [.

{_next = 0; format["%1n", _next];} will -not- crash, showing no error.

I have tried changing things around, tried it in unscheduled space, tried defining the variable, removing the variable, using nil instead of a variable.

Now for the interesting bit:
The crash occurs at the end of scope, not at the offending line.
You can do all kinds of other scripting around the offending line, even bury it in pages of scripting, and all will execute without complaint until the end of the scope.