I have had JRiver configured to start Media Center and Media Server when Windows starts for years and every time I install a major new version of MC (25 > 26, 26 > 27...), I find that the previous version starts up next time Windows is rebooted and I have to disable automatic startup of the old version and re-enable it in the new version. When installing a new version, this is something MC should take care of to ensure that the latest version of MC is started when Windows boots.
When I updated to 27 yesterday, MC26 was still starting automatically and was showing up in the Task Manager > Startup tab. I had to start MC26 and disable the automatic start (which removed MC26 from the Task Manager > Startup tab) and then start MC27, disable the automatic start, and then enable the automatic start again at which point MC27 showed up in the Task Manager > Startup tab. Even though the settings claimed that the "start Media Center and Media Server" option was selected in Options > Startup, Windows wasn't configured to start them until I flipped the setting off and back on.