Resolve FX effects Patch Replace won't cache

When using Resolve 15 Beta 7, when I add a node that does a Patch Replace, the timeline indicates that it has cached the clip (Blue bar) but when you playback it is very slow. This is a big problem for getting my soundtrack correctly synced to the visuals.

My system:
Resolve Version 15.0.0B.073
iMac Pro with macOS 10.13.6

Thanks!