After much sweating I finally found a solution for this and am sharing it here in case other folks stumble upon the same issue.
First, a bit more context: I’m using the “Volumetrics” plug-in to art direct my clouds, I’m indeed using BP_CloudMaskGenerator and BP_CloudMask_Object following [this excellent tutorial][1] from William Faucher.
As said, everything works fine in PIE and launching “as a standalone game” from the editor, but the moment you package, the clouds are gone.
Afaiu, it’s because the CloudMaskGenerator doesn’t get a chance to actually produce its masks and store them in the appropriate Render Targets. The solution I found: in BP_CloudMaskGenerator, in the Event Graph, add a call to BeginPlay followed by “Allocate RTs” and “Render Clouds”: