I'm somewhat confused, if you look at
https://plugins.calibre-ebook.com/ you will see that the plugins name is ScrambleEbook without the space. The calibre code to check for plugin updates uses that site to get the names, not MR. You can see in detail what goes on in calibre, by looking at the read_available_plugins() function and get_installed_status() function in plugin_updater.py
Stick a few print statements in there to see why your plugin is not being detected as installed.