Thanks for the super fast reply!
Yes, I do at least get a refreshed set of ~250 tracks, so it's functionally not a huge deal (still serves the purpose) - was just curious.
I enabled batching and reloaded the extension, but that didn't seem to change anything.
In an act of desperation, I deleted the playlist and re-created it from scratch - and that fixed it!
It's filling as expected now. Strange, but thank you for the help.