Hi Huy!  I disabled all plugins (especially Voxel Toolkit) and retested the live preview.  I think the issue is that our CPT uses repeater fields to build the blog listing page.  When looking at the payload postdata, EA4V only runs on top-level fields.  The repeater’s sub-fields never get processed, no mock attachment ID is created, and the preview renders blank.

I tested this by pulling the image field outside of the repeater and it worked in live-preview.