I don't know what happened, but Diablo 2 is now putting my last played character down the bottom of the selection screen instead of at the top. Has anyone ever encountered this before, or have any idea how to revert it?
But I know that muling utilities, such as ATMA & GoMule both can change the 'last character used' setting, if you opened characters in them - many a good map have been lost this way in my day! Not sure if that is the issue here but it may help!
Is the date on your computer correct? It's not labeling the "last modified" date as last year or something like that, is it?
I have no idea if that would actually cause the problem you are experiencing, but it seems logical if it's sorting them to the bottom, as if they haven't been played for a long time. Just thinking out loud I guess.