Manually tagging with MP3tag actually improved things for me, lol. Yeah plays only show up after they are done.
Okay, good luck in figuring things out! Maybe 10.11 will sort things out…

How long did you wait after adding the albums? Maybe another task was still running, like the LUFS extraction (that ffmpeg job you noticed).
Also, the tag parser was improved with 10.9, maybe your tags don’t have a supported format?

I honestly can’t imagine the Playback Reporting plugin causing this behavior, since it should just passively listen to playback events and record them in a separate database.
Regarding it not getting populated, which client were you using for playback? If the client doesn’t send the correct events, playback won’t be recognized by the server.

Interesting, I never had any issues with the plugin! Are you sure it’s the reason?