ProRes and H.264 Sluggish

I downloaded a demo of the new Sony F's (H.264) from Vimeo and it literally grinds Resolve to a halt.
Alexa ProRes 422HQ footage is nearly as bad.

On the other hand, I can play Blackmagic DNG's at full speed in Resolve, even with extensive grading, without a hiccup.

ArriRaw files also play at full speed, and even Aaton RAW DNG's (much bigger files) play at around 17fps.

In addition, both the Sony and Alexa clips play, with audio, at full speed in Premiere Pro on the same machine.

Any suggestions?

Thanks.