I’m also seeing this issue and its so significant it basically means that we can’t upgrade our project to 5.5.1 until we find a workaround for this.
So far its reproducible with a static mesh component that has the static mesh set on child blueprints, but it only occurs in WorldPartitioned levels in a packaged build.
Not really sure how to debug this either… I’ll probably start throwing some logging in the serialization during cooks, but given that it works in non-world partitioned levels makes it seem to me like its actually a world partition issue with loading an actor.