Odd. Maybe a bug in the latest SMF? I ran all the maintenance stuff I could and was told everything is fine and dandy.
Indeed, I just tried up to member 'start' query of 3479, it works.
Seems to start giving that error after 3480 and above.
/index.php?action=mlist;sort=real_name;start=3479
Seems to never show more or less even decreasing down to 3420