The sent/received metadata but with the actual messages missing on the USSS agents' phones could have two possible explanations:
1. They were using a messaging app with the disappearing / exploding messages feature turned on. Most of the popular encrypted messaging apps have this option.
2. If not option 1 - whether they used an encrypted messenger or regular SMS, the messages were specifically and intentionally deleted.
@Klaatu_Veratta_Nectarine
Sort of, but I was thinking of Signal, Keybase, Wire, etc.