When a cache fails to start (e.g. because a store is not available on startup), the cache is not registered in DefaultCacheManager's map, and stopping the cache manager does not stop any of the components that already started (or even the component that failed).
E.g. in NonStringKeyPreloadTest, the store is not available on startup, and the threads created by HikariCP on startup (in 9.4.x) are not released. The test also leaks an Agroal thread on master, but that is because the test is keeping the connection pool factory in a static field.