FacetWP works well with WP Rocket 3.8+ with the following tweaks.

1. Browse to Settings > WP Rocket and click on the “File Optimization” tab.

2. Click the “Load JavaScript deferred” box and add the following:

*facetwp*

3. Finally, click the “Delay JavaScript execution” box and add the following:

(.*)facetwp(.*)

The result will look like this:

4. If you have CDN enabled, add the following to the “Exclude files from CDN” box:

(.*)facetwp(.*)