@AndySylvester I have no insight into what's going on behind the scenes, but I do see your plugin.json file is missing a semicolon at the end of line 4. Micro.blog is probably choking on that and that's why your plug-in won't update.

When you make changes via DesignEdit Custom Themes they will be reflected right away because you're circumventing GitHub altogether. But the changes are local to your account. Other users who installed the plug-in won't see the changes you make there.