Audio playback is sluggish in Source window

So the audio is actually playing back fine (talking specifically about .wav files, music tracks in particular), but the audio meters are only showing the levels for certain beats in a choppy way, the playhead is sluggish & several frames behind, and it takes a few beats to stop playing after I hit stop. Even when I go frame by frame, the audio comes out of the speakers about a second after I press the advance button.

It's making my audio mixing workflow really clunky and I'm struggling to identify the issue. This seems to be an issue only in the Source window... when I pull anything into the timeline, it all plays smoothly and in realtime, but that's a bit of an impediment to my preferred workflow. Making it work, but would love to identify what's going awry...

(Also, this is only an audio issue, specifically with music tracks; picture seems fine.)

I am working off an external SSD, with nearly 1TB of space remaining.

My RAM is looking good, I don't have a lot of stuff open and I've tried clearing caches and restarting. 

I'm using Mercury Playback Engine GPU Acceleration (OpenCL). Premiere cc 2019, all updated. 

Audio files are .WAV, 48000hz. Any other info that wouold be useful to know?