The FStructPropertyParams::Offset was changed from int32 to uint16 in 5.3. You could have looked that up on your own and reverted it in your own fork
https://github.com/EpicGames/UnrealEngine/blame/4a7ecdab44b9107dbd06cacc4929c3dad3b4d3f4/Engine/Source/Runtime/CoreUObject/Public/UObject/UObjectGlobals.h#L3368
But you seem to have an alternative solution
Why is your class that big in the first place. UObject only has like ~100 ish byte. So getting to 65k is quite the achievement.