Make a backup of your project before following this guide!

Projects using engine versions older the 5.4 follow the guides linked below before this guide
https://defusestudios.com/sgkv2documentation/#Engine-Upgrade

Upgrade from UE5.4 to UE5.5

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Open your project in UE 5.4, in the Content Browser open the S_ItemDetails then click the Default Values tab.

If the World Class is set to None you do not need to follow the steps below, just open your project using Unreal Engine 5.5. If your World Class is not set to None then follow the steps below.

Open your project in Unreal Engine 5.4 then copy the video below.

Then click the Save All button in the Content Browser then close and reopen the project again using Unreal Engine 5.4 then copy the video below.

Note – Don’t worry if your items in the level disappar, after reopening the project they will reappear.

Then click the Save All button in the Content Browser and close the project, you can now open the project using Unreal Engine 5.5.