Many thanks for your feedback! Following it up, we have fixed some performance issues in the IntelliJ-platform plugin, and a problem that was preventing the plugin from detecting Mercurial-based projects: UP-4078.
Next time you start your IDE, it should show you a notification about availability of the new version of Upsource integration plugin. Alternatively, you can update the plugin from Preferences | Plugins.
If there are any other issues you’ve been experiencing, do not hesitate to share them with us via firstname.lastname@example.org.