FYI this is still happening. Been sitting here for about an hour trying to figure out what the problem was and then I finally just copy and pasted the error in to google and found this post.
I removed the line “GameMesh->SetMassOverrideInKg(“None”, 100.0f, true);” and the game packages perfectly fine now.
I wrote that line a few days ago and just forgot all about that. But the error for this is so vague it’s really hard to track down.