Multiple on-board backup locations of numerous video sensors means unless the entire vehicle is torched (and even then), some evidence of the people who carried out the theft will probably survive.
When talking about autonomous platforms, a jammer might no longer be sufficient. If communication is lost, how hard is it to launch a drone (or multiple) whose job it is to keep visual contact with the vehicle while increasing distance, and relay the feed up when communication is re-established (how large an area does a jammer affect?).
There are ways to mitigate these defenses/logging (reduce all unique visuals, stop vehicle in tunnel), but also ways to minimize those mitigations.
I'm not sure it's any easier than when a human is present to defend the goods.
That's no fun for the ICE 20 miles out.
It certainly is something that I think of, but safety engineering requires simpler processes (because simpler means less things need to go right, which is good when things are breaking). I'd rather pay more for cargo insurance than have more complicated logic that causes more accidents with people.