Gradual freeze at random

This is a random occurrence about once every 20 hours of operation on WiFi Netflix.
First the video freezes but audio plays on for about 10 seconds, then PPM locks solid.
If I move fast enough (before the audio stops) I can power down normally, then power back on as usual.
If it hangs all the way, a hard reset holding the power button brings it back around again.
Not related to overheating, as neither PPM nor exhaust air is overly hot, and once it’s power-cycled it runs just fine.