I just spent ages trying to work out why my crashlytics stopped sending in iOS, it turned out it was to do with this https://github.com/invertase/react-native-firebase/issues/3879, but working out what was going on took ages.
It would have helped a lot if I could have turned on a logging mode so that I could see more info about crashes that were recorded and if they were sent or not. It would also be really useful to see something like not sent because logging is turned off by default.