RestEasy's current Server Sent Events design will continually reconnect after events are sent, causing the same events to be sent repeatedly until the SseEventSource is closed.
See Pull request #2687: I've added a test variation (testSseEventSourceCountDownOnCompleteCallback) to SseEventSourceTest.java. In this testcase the CountDownLatch is not closed until the OnComplete event is received. Running this test will result in the single event to be sent over an over again until the latch times out. In my sandbox the event was re-sent 60 times. This behavior is different from what occurs on CXF or WebSphere Liberty.