I've noticed this a few times now: I come back to a map after a while (today's was at least a couple months, and I had to unarchive it, but this has happened with non-archived maps after a few days), and all the text that was on the GM layer is just gone. Everything else is there - tokens, lines, boxes. But anything added using the text tool is just gone. It isn't an issue of the text not saving because I used the map multiple times in different sessions and the text was there. It's just gone a couple months later.