This happened with my 722 last night. Mine is configured to start a new file on drive error so it kept rolling but I have not checked yet. It happened twice. If the software was written properly, there should not be any glitch between the two files as long as the time to start a new file is less than the size of the pre-roll buffer. When I get a chance to open the files tonight, I'll know. I had the unit locked. It displayed the error message and then cleared the error message when I started the unlock sequence. I recall that the new take was about 8 minutes in, so maybe my files are OK. (This is what I remember, I was nodding off during the entire show).
After originally reading this thread, I reformated my drive. I've done 6 or so sessions since the format operation and they were all sequentially recorded with no files deleted from the unit since the format. There should be 0% fragmentation, so that is not an excuse for the behavior on my machine. One thing that came to mind last night is that I did not see this issue before I upgraded to the recent firmware and before this thread raised my concern about fragmentation, I was selectively removing little files before recording new takes and generally doing everything to cause fragmentation.