Recently, I passed for a problem when I needed run a project, for my surprise, I run yarn android and I receive this message:

Starting a Gradle Daemon, 1 busy and 6 stopped Daemons could not be reused, use --status for details

The problem is, the simulator spend a lot time and never show up, and then, Googling I found the solution, is simple, just run:

gradle --stop

Done!