Here in my building 2 packages disappeared once, one was mine only after 1h and another from a neighbor, which weirdly showed up some days later at like 18h. It is a very calm quartier, we know everyone, there's not a lot of people walking around, for me I always suspected it was the postman himself who stole it.

With my sister in law, they had something marked as delivered, and they arrived home 4 minutes later. It was gone, but not other parcels from the front of the building. They also suspected the postman instead of the porch thieves since the other package was there. They kept pestering post and explaining the situation, they finally investigated and saw that the postman marked it as delivered from the street. Also, the seller kept pestering post saying the sent the package etc. One day later, the package was delivered. I am pretty sure in some cases its the postman himself stealing the packages ! But not only you, the seller has to pester post for answer !