Go to the BP_SGKSaveGame and create a new variable called TempItemSpawnerSaveData and set its type to S_ItemSpawnerSave then set the variable type to Array.

Next go to the SaveItemSpawners function in the BP_SGKSaveGame and copy the images below.

Copy the video below

Then go to the BP_SaveSystem and then to the Saving collapsed node in the Event Graph and copy the image below.

To add the ItemSpawnerSaveData to the Set members in S_LevelSaveData node click it and in the details panel tick on the ItemSpawnerSaveData tick box.