FT8 protocol question: F/H DX operation
I'm hoping someone here can answer a question I have about the FT8 protocol.
While monitoring a DXpedition using fox/hound mode (F/H) I observed the fox (H44WA, Solomon Islands) sending occasional FT8 "free text" messages that I have not seen before. I'm wondering if someone can tell me what these are. I did a bunch of Googling and even looked at the source code to MSHV, but couldn't find any explanation.
Look at the image below. You can see the hounds calling above followed by the fox acknowledgements below. One in standard message format (msg = 1.0), a report to 4Z5PJ. Then a DX message format (msg = 0.1) with an RR73 to HL5QY and a report to HK30.
But then there is this third message in free text format (msg = 0.0) that has the fox's call and a 6-digit number. These are not sent on each fox exchange. Only occasionally. And the number usually increments by a large random amount (10's to 100's of thousands), but not always.
Does this have something to do with an associated logging program? The number value is too random to be some sort of logging serial number.