I had a similar situation but when trying to return an S23 to Samsung. I got a video showing that the phone wasn’t there anymore. They left the box and took the return sheet and the phone. It was also via FedEx.

They sent me a video from Samsung showing the opening of the box and the tape looks evidently that it’s been tampered. When they opened the box, everything is in disarray and the box is empty.

I reported it to Samsung right away and they said they are investigating, so based on what you said they’ll likely ask me to file a police report. I dropped it off at a local FedEx store. This sounds like very targeted crime since they know how to recognize the boxes.