Moved from 5.1 to 5.3, can't package (cooking): on-optional object (x:x_ECEditorOnlyData) has a reference to optional object (x:xEditorOnlyData)

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Hi, while packaging I have the following error after moving from 5.1 to 5.3:

Error: Can’t save D:/MyProjects/Unreal/EternalCrusadeResurrection53/Saved/Cooked/Windows/ECR/Content/VFX/Water/M_UnderWater_PostProcess_Volume_Carmine.uasset: Non-optional object (/Game/VFX/Water/M_UnderWater_PostProcess_Volume_Carmine.M_UnderWater_PostProcess_Volume_Carmine:M_UnderWater_PostProcess_Volume_ECEditorOnlyData) has a reference to optional object (/Game/VFX/Water/M_UnderWater_PostProcess_Volume_Carmine.M_UnderWater_PostProcess_Volume_Carmine:M_UnderWater_PostProcess_Volume_CarmineEditorOnlyData). Only optional objects can refer to other o
ptional objects.

Which prevents cooking.

This was actually a MI I created from water material in water plugin.