This packaging issue from 4.16 is still around in 4.17.2: https://answers.unrealengine.com/questions/604591/packaging-error-ensure-condition-failed-getsupercl.html
If the ensures in UBlueprintGeneratedClass::NeedsLoadForServer were removed, the package would work fine (I had done this in 4.17.1 with a custom engine build).
It would be nice to get a hand with this one. Cheers!