Choppy multicam playback even with Proxy files

Three camera shoot in 4K30 10 bit on one cam, 4K 30 8 on the others. Proxys built for all files and linked. Even tried reducing timeline proxy res. to 1/4 and still have choppy playback in both multicam viewer and main viewer. Have done similar projects with smooth playback. Only difference is past projects were all 8 bit.

Pretty beefy setup with i9 9900K at 32GB and Nvidia RTX 3070. Resolve version is 18.1.2

Really scratching my head on this one.

What proxy resolution and codec did you select?

DNXhr SQ 1/4

Think I figured it out. One of the four tracks was a downloaded Youtube stream file. Since it was only 1080P and a fairly low bitrate, I thought a proxy was unnecessary. With this track disabled, Resolve runs fine. It's my guess that this file is so aggressively compressed that this is what caused the timeline choppiness.