I don't have any other issues with java and STS starts up fine but when I try to run my app as "Run as Spring Boot App" (or any of the samples), the console is empty for up to 5 minutes, before I get the familiar "Spring Boot" ASCII art. Then it works fine.
Turns out there was an issue resolving the network host. I fixed it by executing this command from the console:
scutil --set HostName "localhost"