It's not just certain environments, I'm fairly sure that if you use a normal promise polyfill like babel-polyfill provides, then unhandled promise rejection fai

It's not just certain environments, I'm fairly sure that if you use a normal promise polyfill like babel-polyfill provides, then unhandled promise rejection failures will always trigger window.onunhandledrejection, which is analogous to window.onerror (unhandled promise rejections in async code are the equivalent of unhandled exceptions in sync code). If you set up both of those to do any error handling/reporting that you need, you can avoid any issues of promise rejections getting swallowed.