@Aceeee82 I think I found a solution. The household actually is neither in my nor in other households and I believe that's what's causing the issue for you.
Follow these steps
1. Load your save with Load instead of resume
2. Go to del sol valley, select the family and the click on Evict in the lower right corner.
3. Go to the household manager and find them in other households (best to sort by name and then just scroll down)
4. Move them back into the lot
5. Save the game under a new name
6. Travel for example to the park in Oasis Spring
7. Either go fishing, catch frogs or get a collectible some other way.
8. Travel home
9. The collected object should now still be in your inventory.
(Steps 6-9 are only to test if it works. Steps 1-4 should fix the issue)
