Apparently the movement from the old server to the new one resulted in time zone change and altered mail server as well . This has impacted the internal sorting of your PM items.
I recommend every NG member to purge all PM entries so as to avoid searching for "missing" messages. They are not really missing, only misplaced, but if you have a long series of such entries, finding a particular one can be troublesome. Better to purge the list and start afresh.
