I have repeatedly complained that SE19 Java debugging is broken and also filed a case with support, all with little traction. SE17 was the last release where Java debugging worked reliably, but that's of no help since it does not support Java 8.
So, here is one more attempt to put a spotlight on the problem, which is that the SE Java debugger no longer shows when the debugee hits a breakpoint. It may work properly for a few times but then it no longer processes a JWDP breakpoint event and the debug UI acts as if the debugee is still running while it is really suspended. I can coerce the UI to show the breakpoint by doing something seemingly unrelated such as setting another breakpoint somewhere in the code.
To experience the problem, use the attached sample project. Set a breakpoint at line 11, then debug run (F5) the program. It should hit the breakpoint about once a second. Continue to hit F5 when the breakpoint is reached (watch the status line at the bottom). Continue pressing F5 until the program no longer stops. It takes me anywhere from 2-10 F5's until it freezes.
You can then set/clear a breakpoint at line 15. This will unleash the debugger and it will stop at line 11 and give you one more opportunity to press F5. Nonsensical, but I do this a lot just to get some primitive testing done.
Attached is the sample project, a copy of the JWDT trace, and a recording of the bug.
Marcel