I saw a report of this in another forum, but figured it might be good to have here. I'm running macOS 10.13.2, PlexAmp 1.0.2 (same with 1.0.1). PlexAmp works correctly with a local player, but when using my remote Mac mini player it fails to show a now playing screen. Controlling playback (stop / start) and selection screens still work though.
I saw a similar report regarding the Windows client, so it seems to be a cross-platform issue.
Have reinstalled a few times, did a total wipe of ~/Library/Applications Support/Plexamp and preference files as well. No dice.