This issue drove me crazy still in 2019, but I think I finally figured out, what did the exception cause.
I followed all the setup instructions given in the official firebase documentation, but when I tested my solution I didn’t get any report on Firebase Crashlytics admin, because of the TimeoutException.
The reason was in my case, that I triggered the Exception in my main activity’s onCreate() or onResume() methods.
When I let my app at the first start just run without exception, then later I started to get the reports without any error, so I think it’s important, that at the first start the app shouldn’t throw any exception in the hook methods.
Hope my experience helped.