This is unfortunately a know issue with the new spring-boot-devtools module (see https://github.com/spring-projects/spring-boot/issues/3100). We use this trick to kill the main thread so that we can replace it with a re-loadable version. So far I’ve not found a way to prevent the debug breakpoint from triggering.
For now, you can toggle the “suspend execution on uncaught exceptions” checkbox in Java -> Debug preferences to prevent it from happening.