Slots are UObjects, but they are not registered as property.
Which means eventually they are going to be garbage collected.
If you keep an instance to use the whole runtime session, there’s a point where Unreal will destroy the object and leave you with a dead pointer.
So you should treat slots as temporary objects and not a database.
The data is erased to prevent memory leaks after save.
I could make slots persistent and not collectible by GC, but that’s not the default behavior for any save system.