I’ve been having a chronic issue where quitting Spark closes the Spark window, but doesn’t quit the Spark.exe process, so when I want to open Spark again I have to open Task Manager and manually quit the process. I’m currently running Spark 2.6.0 on Windows 7 Enterprise, and this problem started with Spark 2.5.8. There’s no error in Event Viewer.
I’ve also had the same problem. When I killed the process in task manager, Openfire logged an Exception about the disconnection, so there was clearly a thread connected to the server, but there was no GUI visible.