The household inventory is tied to a household and not a a Sim.
So if you move into a new household (either by creating a new empty one or by moving into someone else's household, you loose the inventory.
There should be no issues if you use the move interaction on the phone but as soon as you use the household one, you need to pay attention what you do
So the left hand side (1) is what's keeping the current inventory. The right hand side (2) either has the inventory of the Sim your moving into or none if create a new household.
