TheDude recently upgraded the server to the most recent version of Lemmy. You'll notice significant improvements to the user interface, and hopefully the functionality is also improved. There is no official changelog yet because this version is not yet finalized, but I'll link the GitHub releases page where it should eventually appear.
https://github.com/LemmyNet/lemmy/releases
Edit: 0.18.1 is now fully released and we have upgraded to the final version. You can view the link above for the changelog.
Yes seems that hot and active just don't show old posts anymore. Inactive commmunities appeear "empty" now.